Encoder, a decoder and corresponding methods related to intra prediction mode

ABSTRACT

A method of coding implemented by a decoding device or an encoding device, comprising obtaining indication information for a luma position (cbWidth/2, cbHeight/2) of a current coding block, relative to a top-left luma sample position (xCb, yCb) of the current coding block; setting a value of a luma intra prediction mode associated with the current coding block to a first default value, when the indication information indicates that an Intra Block Copy (IBC) mode or palette mode is applied for the luma component at the luma position (cbWidth/2, cbHeight/2), relative to the top-left luma sample position (xCb, yCb) of the current coding block; and obtaining a value of a chroma intra prediction mode based on the value of the luma intra prediction mode of the current coding block.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/478,534, filed on Sep. 17, 2021, which is a continuation ofInternational Application No. PCT/CN2020/102524, filed on Jul. 17, 2020,which claims priority to International Application No.PCT/EP2019/072611, filed on Aug. 23, 2019 and International ApplicationNo. PCT/EP2019/069944, filed on Jul. 24, 2019. All of the aforementionedpatent applications are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

Embodiments of the present application (disclosure) generally relate tothe field of picture processing and more particularly to perform chromaintra prediction mode derivation by using intra prediction mode fromcorresponding luma component.

BACKGROUND

Video coding (video encoding and decoding) is used in a wide range ofdigital video applications, for example broadcast digital TV, videotransmission over internet and mobile networks, real-time conversationalapplications such as video chat, video conferencing, DVD and Blu-raydiscs, video content acquisition and editing systems, and camcorders ofsecurity applications.

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in picture qualityare desirable.

SUMMARY

Embodiments of the present application provide apparatuses and methodsfor encoding and decoding according to the independent claims.

The foregoing and other objects are achieved by the subject matter ofthe independent claims. Further implementation forms are apparent fromthe dependent claims, the description and the figures.

A first aspect of the disclosure relates to a method of codingimplemented by a decoding device or an encoding device. The methodincludes: obtaining indication information for a luma position(cbWidth/2, cbHeight/2) of a current coding block, relative to thetop-left luma sample position (xCb, yCb) of the current coding block,where cbWidth represents a width of the current coding block in a lumacomponent, cbHeight represents a height of the current coding block inthe luma component. Correspondingly, cbWidth/2 represents a half of awidth of the current coding block in a luma component, and cbHeight/2represents a half of a height of the current coding block in the lumacomponent. The absolute position of the luma position (cbWidth/2,cbHeight/2) is (xCb+cbWidth/2, yCb+cbHeight/2), i.e. the ‘middle’ of thecorresponding luma prediction block.

In one embodiment, the method further includes: setting a value of aluma intra prediction mode associated with the current coding block to adefault value, when the indication information indicates that aMatrix-based Intra Prediction, MIP, is applied for the luma component atthe luma position (cbWidth/2, cbHeight/2), relative to the top-left lumasample position (xCb, yCb) of the current coding block; and obtaining avalue of a chroma intra prediction mode based on the value of the lumaintra prediction mode of the current coding block.

Obtaining prediction mode information from a fixed position (cbWidth/2,cbHeight/2) in the corresponding luma component ensures mode MIP'sposition and luma intra prediction mode's position is aligned when in agiven block size, the partition of luma component is different from thepartition of chroma component (e.g. when dual-tree coding method isenabled), where mode MIP's position stands for a position where MIP modeis obtained, and luma intra prediction mode's position stands for aposition where luma intra prediction mode is obtained.

A second aspect of the disclosure relates to a method of codingimplemented by a decoding device or an encoding device. The methodincludes: obtaining indication information for a luma position(cbWidth/2, cbHeight/2) of a current coding block, relative to thetop-left luma sample position (xCb, yCb) of the current coding block,where cbWidth represents a width of the current coding block in a lumacomponent, cbHeight represents a height of the current coding block inthe luma component. Correspondingly, cbWidth/2 represents a half of awidth of the current coding block in a luma component, and cbHeight/2represents a half of a height of the current coding block in the lumacomponent. The absolute position of the luma position (cbWidth/2,cbHeight/2) is (xCb+cbWidth/2, yCb+cbHeight/2), i.e. the ‘middle’ of thecorresponding luma prediction block.

In one embodiment, the method further includes: setting a value of aluma intra prediction mode associated with the current coding block to afirst default value, when the indication information indicates that anIntra Block Copy, IBC, mode or palette mode is applied for the lumacomponent at the luma position (cbWidth/2, cbHeight/2), relative to thetop-left luma sample position (xCb, yCb) of the current coding block;and obtaining a value of a chroma intra prediction mode based on thevalue of the luma intra prediction mode of the current coding block.

Obtaining prediction mode information from a fixed position (cbWidth/2,cbHeight/2) in the corresponding luma component ensures mode IBC'sposition and luma intra prediction mode's position is aligned when in agiven block size, the partition of luma component is different from thepartition of chroma component (e.g. when dual-tree coding method isenabled), where mode IBC's position stands for a position where IBC modeis obtained, and luma intra prediction mode's position stands for aposition where luma intra prediction mode is obtained.

Alternatively, obtaining prediction mode information from a fixedposition (cbWidth/2, cbHeight/2) in the corresponding luma componentensures mode palette's position and luma intra prediction mode'sposition is aligned when in a given block size, the partition of lumacomponent is different from the partition of chroma component (e.g. whendual-tree coding method is enabled), where mode palette's positionstands for a position where palette mode is obtained, and luma intraprediction mode's position stands for a position where luma intraprediction mode is obtained.

The alignment of obtaining mode information from position (cbWidth/2,cbHeight/2) is necessary when in a given block size, the partition ofluma component is different from the partition of chroma component.Otherwise, it might cause undefined behavior as showed in FIG. 7.

In one embodiment, the method according to the first aspect of thedisclosure can be performed by the apparatus according to the thirdaspect of the disclosure. Further features and implementation forms ofthe apparatus according to the third aspect of the disclosure correspondto the features and implementation forms of the method according to thefirst aspect of the disclosure.

In one embodiment, the method according to the second aspect of thedisclosure can be performed by the apparatus according to the fourthaspect of the disclosure. Further features and implementation forms ofthe apparatus according to the fourth aspect of the disclosurecorrespond to the features and implementation forms of the methodaccording to the second aspect of the disclosure.

According to a fifth aspect, the embodiment of the disclosure relates toan apparatus for decoding or encoding a video stream includes aprocessor and a memory. The memory is storing instructions that causethe processor to perform the method according to the first aspect.

According to a sixth aspect, the embodiment of the disclosure relates toan apparatus for decoding or encoding a video stream includes aprocessor and a memory. The memory is storing instructions that causethe processor to perform the method according to the second aspect.

According to a seventh aspect, a computer-readable storage medium havingstored thereon instructions that when executed cause one or moreprocessors configured to code video data is proposed. The instructionscause the one or more processors to perform a method according to thefirst or second aspect or any possible embodiment of the first or secondaspect.

According to an eighth aspect, the embodiment of the disclosure relatesto a computer program comprising program code for performing the methodaccording to the first or second aspect or any possible embodiment ofthe first or second aspect when executed on a computer.

According to a ninth aspect, the embodiment of the disclosure relates toa device for obtaining chroma intra prediction mode, comprising: one ormore processors; and a non-transitory computer-readable storage mediumcoupled to the processors and storing programming for execution by theprocessors, wherein the programming, when executed by the processors,configures the decoder to: obtain first indication information for aluma position (cbWidth/2, cbHeight/2) of a current coding block,relative to a top-left luma sample position (xCb, yCb) of the currentcoding block, wherein cbWidth represents a width of the current codingblock in a luma component, cbHeight represents a height of the currentcoding block in the luma component. Correspondingly, cbWidth/2represents a half of a width of the current coding block in a lumacomponent, and cbHeight/2 represents a half of a height of the currentcoding block in the luma component. The absolute position of the lumaposition (cbWidth/2, cbHeight/2) is (xCb+cbWidth/2, yCb+cbHeight/2),i.e. the ‘middle’ of the corresponding luma prediction block.

In one embodiment, the one or more processors further configured to seta value of a luma intra prediction mode associated with the currentcoding block to a first default value, when the first indicationinformation indicates that a Matrix-based Intra Prediction, MIP, isapplied for the luma component at the luma position (cbWidth/2,cbHeight/2), relative to the top-left luma sample position (xCb, yCb) ofthe current coding block; or obtain second indication information forthe luma position (cbWidth/2, cbHeight/2) of the current coding block,when the first indication information indicates that the MIP is notapplied for the luma component at the luma position (cbWidth/2,cbHeight/2), relative to the top-left luma sample position (xCb, yCb) ofthe current coding block.

In one embodiment, the one or more processors further configured to setthe value of the luma intra prediction mode associated with the currentcoding block to a second default value when the second indicationinformation indicates that an Intra Block Copy (IBC) mode or palettemode is applied for the luma component at the luma position (cbWidth/2,cbHeight/2), relative to the top-left luma sample position (xCb, yCb) ofthe current coding block; and obtain a value of a chroma intraprediction mode based on the value of the luma intra prediction mode ofthe current coding block.

Obtaining first indication information from a fixed position (cbWidth/2,cbHeight/2) in the corresponding luma component ensures mode MIP'sposition and luma intra prediction mode's position is aligned when in agiven block size, the partition of luma component is different from thepartition of chroma component (e.g. when dual-tree coding method isenabled). When the first indication information does not indicate thatMIP is applied for the luma component at the luma position (cbWidth/2,cbHeight/2), obtaining second indication information from a fixedposition (cbWidth/2, cbHeight/2) in the corresponding luma componentensures mode IBC's position and luma intra prediction mode's position isaligned when in a given block size, the partition of luma component isdifferent from the partition of chroma component (e.g. when dual-treecoding method is enabled). Alternatively, obtaining second indicationinformation from a fixed position (cbWidth/2, cbHeight/2) in thecorresponding luma component ensures mode palette's position and lumaintra prediction mode's position is aligned when in a given block size,the partition of luma component is different from the partition ofchroma component (e.g. when dual-tree coding method is enabled).

Details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the disclosure are described in moredetail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding systemconfigured to implement embodiments of the disclosure;

FIG. 1B is a block diagram showing another example of a video codingsystem configured to implement embodiments of the disclosure;

FIG. 2 is a block diagram showing an example of a video encoderconfigured to implement embodiments of the disclosure;

FIG. 3 is a block diagram showing an example structure of a videodecoder configured to implement embodiments of the disclosure;

FIG. 4 is a block diagram illustrating an example of an encodingapparatus or a decoding apparatus;

FIG. 5 is a block diagram illustrating another example of an encodingapparatus or a decoding apparatus;

FIG. 6 shows an example about intra prediction modes.

FIG. 7 is a block diagram illustrating the potential problem of anundefined behavior in chroma intra prediction mode derivation using thecurrent specification.

FIG. 8 shows an example about luma location value of a coding block.

FIG. 9 illustrates embodiments of method 900 according to the presentdisclosure.

FIG. 10 illustrates embodiments of a device 1000 for use according tothe present disclosure.

FIG. 11 is a block diagram showing an example structure of a contentsupply system 3100 which realizes a content delivery service.

FIG. 12 is a block diagram showing a structure of an example of aterminal device.

In the following identical reference signs refer to identical or atleast functionally equivalent features if not explicitly specifiedotherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanyingfigures, which form part of the disclosure, and which show, by way ofillustration, specific aspects of embodiments of the disclosure orspecific aspects in which embodiments of the present disclosure may beused. It is understood that embodiments of the disclosure may be used inother aspects and comprise structural or logical changes not depicted inthe figures. The following detailed description, therefore, is not to betaken in a limiting sense, and the scope of the present disclosure isdefined by the appended claims.

For instance, it is understood that a disclosure in connection with adescribed method may also hold true for a corresponding device or systemconfigured to perform the method and vice versa. For example, if one ora plurality of specific method operations are described, a correspondingdevice may include one or a plurality of units, e.g. functional units,to perform the described one or plurality of method operations (e.g. oneunit performing the one or plurality of operations, or a plurality ofunits each performing one or more of the plurality of operations), evenif such one or more units are not explicitly described or illustrated inthe figures. On the other hand, for example, if a specific apparatus isdescribed based on one or a plurality of units, e.g. functional units, acorresponding method may include one operation to perform thefunctionality of the one or plurality of units (e.g. one operationperforming the functionality of the one or plurality of units, or aplurality of operations each performing the functionality of one or moreof the plurality of units), even if such one or plurality of operationsare not explicitly described or illustrated in the figures. Further, itis understood that the features of the various exemplary embodimentsand/or aspects described herein may be combined with each other, unlessspecifically noted otherwise.

Video coding typically refers to the processing of a sequence ofpictures, which form the video or video sequence. Instead of the term“picture” the term “frame” or “image” may be used as synonyms in thefield of video coding. Video coding (or coding in general) comprises twoparts video encoding and video decoding. Video encoding is performed atthe source side, typically comprising processing (e.g. by compression)the original video pictures to reduce the amount of data required forrepresenting the video pictures (for more efficient storage and/ortransmission). Video decoding is performed at the destination side andtypically comprises the inverse processing compared to the encoder toreconstruct the video pictures. Embodiments referring to “coding” ofvideo pictures (or pictures in general) shall be understood to relate to“encoding” or “decoding” of video pictures or respective videosequences. The combination of the encoding part and the decoding part isalso referred to as CODEC (Coding and Decoding).

In case of lossless video coding, the original video pictures can bereconstructed, i.e. the reconstructed video pictures have the samequality as the original video pictures (assuming no transmission loss orother data loss during storage or transmission). In case of lossy videocoding, further compression, e.g. by quantization, is performed, toreduce the amount of data representing the video pictures, which cannotbe completely reconstructed at the decoder, i.e. the quality of thereconstructed video pictures is lower or worse compared to the qualityof the original video pictures.

Several video coding standards belong to the group of “lossy hybridvideo codecs” (i.e. combine spatial and temporal prediction in thesample domain and 2D transform coding for applying quantization in thetransform domain). Each picture of a video sequence is typicallypartitioned into a set of non-overlapping blocks and the coding istypically performed on a block level. In other words, at the encoder thevideo is typically processed, i.e. encoded, on a block (video block)level, e.g. by using spatial (intra picture) prediction and/or temporal(inter picture) prediction to generate a prediction block, subtractingthe prediction block from the current block (block currentlyprocessed/to be processed) to obtain a residual block, transforming theresidual block and quantizing the residual block in the transform domainto reduce the amount of data to be transmitted (compression), whereas atthe decoder the inverse processing compared to the encoder is applied tothe encoded or compressed block to reconstruct the current block forrepresentation. Furthermore, the encoder duplicates the decoderprocessing loop such that both will generate identical predictions (e.g.intra- and inter predictions) and/or re-constructions for processing,i.e. coding, the subsequent blocks.

In the following embodiments of a video coding system 10, a videoencoder 20 and a video decoder 30 are described based on FIGS. 1 to 3.

FIG. 1A is a schematic block diagram illustrating an example codingsystem 10, e.g. a video coding system 10 (or short coding system 10)that may utilize techniques of this present application. Video encoder20 (or short encoder 20) and video decoder 30 (or short decoder 30) ofvideo coding system 10 represent examples of devices that may beconfigured to perform techniques in accordance with various examplesdescribed in the present application.

As shown in FIG. 1A, the coding system 10 comprises a source device 12configured to provide encoded picture data 21 e.g. to a destinationdevice 14 for decoding the encoded picture data 13.

The source device 12 comprises an encoder 20, and may additionally, i.e.optionally, comprise a picture source 16, a pre-processor (orpre-processing unit) 18, e.g. a picture pre-processor 18, and acommunication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturingdevice, for example a camera for capturing a real-world picture, and/orany kind of a picture generating device, for example a computer-graphicsprocessor for generating a computer animated picture, or any kind ofother device for obtaining and/or providing a real-world picture, acomputer generated picture (e.g. a screen content, a virtual reality(VR) picture) and/or any combination thereof (e.g. an augmented reality(AR) picture). The picture source may be any kind of memory or storagestoring any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed bythe pre-processing unit 18, the picture or picture data 17 may also bereferred to as raw picture or raw picture data 17.

Pre-processor 18 is configured to receive the (raw) picture data 17 andto perform pre-processing on the picture data 17 to obtain apre-processed picture 19 or pre-processed picture data 19.Pre-processing performed by the pre-processor 18 may, e.g., comprisetrimming, color format conversion (e.g. from RGB to YCbCr), colorcorrection, or de-noising. It can be understood that the pre-processingunit 18 may be optional component.

The video encoder 20 is configured to receive the pre-processed picturedata 19 and provide encoded picture data 21 (further details will bedescribed below, e.g., based on FIG. 2).

Communication interface 22 of the source device 12 may be configured toreceive the encoded picture data 21 and to transmit the encoded picturedata 21 (or any further processed version thereof) over communicationchannel 13 to another device, e.g. the destination device 14 or anyother device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g. a video decoder30), and may additionally, i.e. optionally, comprise a communicationinterface or communication unit 28, a post-processor 32 (orpost-processing unit 32) and a display device 34.

The communication interface 28 of the destination device 14 isconfigured receive the encoded picture data 21 (or any further processedversion thereof), e.g. directly from the source device 12 or from anyother source, e.g. a storage device, e.g. an encoded picture datastorage device, and provide the encoded picture data 21 to the decoder30.

The communication interface 22 and the communication interface 28 may beconfigured to transmit or receive the encoded picture data 21 or encodeddata 13 via a direct communication link between the source device 12 andthe destination device 14, e.g. a direct wired or wireless connection,or via any kind of network, e.g. a wired or wireless network or anycombination thereof, or any kind of private and public network, or anykind of combination thereof.

The communication interface 22 may be, e.g., configured to package theencoded picture data 21 into an appropriate format, e.g. packets, and/orprocess the encoded picture data using any kind of transmission encodingor processing for transmission over a communication link orcommunication network.

The communication interface 28, forming the counterpart of thecommunication interface 22, may be, e.g., configured to receive thetransmitted data and process the transmission data using any kind ofcorresponding transmission decoding or processing and/or de-packaging toobtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may beconfigured as unidirectional communication interfaces as indicated bythe arrow for the communication channel 13 in FIG. 1A pointing from thesource device 12 to the destination device 14, or bi-directionalcommunication interfaces, and may be configured, e.g. to send andreceive messages, e.g. to set up a connection, to acknowledge andexchange any other information related to the communication link and/ordata transmission, e.g. encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 andprovide decoded picture data 31 or a decoded picture 31 (further detailswill be described below, e.g., based on FIG. 3 or FIG. 5).

The post-processor 32 of destination device 14 is configured topost-process the decoded picture data 31 (also called reconstructedpicture data), e.g. the decoded picture 31, to obtain post-processedpicture data 33, e.g. a post-processed picture 33. The post-processingperformed by the post-processing unit 32 may comprise, e.g. color formatconversion (e.g. from YCbCr to RGB), color correction, trimming, orre-sampling, or any other processing, e.g. for preparing the decodedpicture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 is configured toreceive the post-processed picture data 33 for displaying the picture,e.g. to a user or viewer. The display device 34 may be or comprise anykind of display for representing the reconstructed picture, e.g. anintegrated or external display or monitor. The displays may, e.g.comprise liquid crystal displays (LCD), organic light emitting diodes(OLED) displays, plasma displays, projectors, micro LED displays, liquidcrystal on silicon (LCoS), digital light processor (DLP) or any kind ofother display.

Although FIG. 1A depicts the source device 12 and the destination device14 as separate devices, embodiments of devices may also comprise both orboth functionalities, the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality. In such embodiments the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality may be implemented using the same hardware and/or softwareor by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, theexistence and (exact) split of functionalities of the different units orfunctionalities within the source device 12 and/or destination device 14as shown in FIG. 1A may vary depending on the actual device andapplication.

The encoder 20 (e.g. a video encoder 20) or the decoder 30 (e.g. a videodecoder 30) or both encoder 20 and decoder 30 may be implemented viaprocessing circuitry as shown in FIG. 1B, such as one or moremicroprocessors, digital signal processors (DSPs), application-specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),discrete logic, hardware, video coding dedicated or any combinationsthereof. The encoder 20 may be implemented via processing circuitry 46to embody the various modules as discussed with respect to encoder 20 ofFIG. 2 and/or any other encoder system or subsystem described herein.The decoder 30 may be implemented via processing circuitry 46 to embodythe various modules as discussed with respect to decoder 30 of FIG. 3and/or any other decoder system or subsystem described herein. Theprocessing circuitry may be configured to perform the various operationsas discussed later. As shown in FIG. 5, if the techniques areimplemented partially in software, a device may store instructions forthe software in a suitable, non-transitory computer-readable storagemedium and may execute the instructions in hardware using one or moreprocessors to perform the techniques of this disclosure. Either of videoencoder 20 and video decoder 30 may be integrated as part of a combinedencoder/decoder (CODEC) in a single device, for example, as shown inFIG. 1B.

Source device 12 and destination device 14 may comprise any of a widerange of devices, including any kind of handheld or stationary devices,e.g. notebook or laptop computers, mobile phones, smart phones, tabletsor tablet computers, cameras, desktop computers, set-top boxes,televisions, display devices, digital media players, video gamingconsoles, video streaming devices(such as content services servers orcontent delivery servers), broadcast receiver device, broadcasttransmitter device, or the like and may use no or any kind of operatingsystem. In some cases, the source device 12 and the destination device14 may be equipped for wireless communication. Thus, the source device12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in FIG. 1A is merelyan example and the techniques of the present application may apply tovideo coding settings (e.g., video encoding or video decoding) that donot necessarily include any data communication between the encoding anddecoding devices. In other examples, data is retrieved from a localmemory, streamed over a network, or the like. A video encoding devicemay encode and store data to memory, and/or a video decoding device mayretrieve and decode data from memory. In some examples, the encoding anddecoding is performed by devices that do not communicate with oneanother, but simply encode data to memory and/or retrieve and decodedata from memory.

For convenience of description, embodiments of the disclosure aredescribed herein, for example, by reference to High-Efficiency VideoCoding (HEVC) or to the reference software of Versatile Video coding(VVC), the next generation video coding standard developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).One of ordinary skill in the art will understand that embodiments of thedisclosure are not limited to HEVC or VVC.

Encoder and Encoding Method

FIG. 2 shows a schematic block diagram of an example video encoder 20that is configured to implement the techniques of the presentapplication. In the example of FIG. 2, the video encoder 20 comprises aninput 201 (or input interface 201), a residual calculation unit 204, atransform processing unit 206, a quantization unit 208, an inversequantization unit 210, and inverse transform processing unit 212, areconstruction unit 214, a loop filter unit 220, a decoded picturebuffer (DPB) 230, a mode selection unit 260, an entropy encoding unit270 and an output 272 (or output interface 272). The mode selection unit260 may include an inter prediction unit 244, an intra prediction unit254 and a partitioning unit 262. Inter prediction unit 244 may include amotion estimation unit and a motion compensation unit (not shown). Avideo encoder 20 as shown in FIG. 2 may also be referred to as hybridvideo encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206,the quantization unit 208, the mode selection unit 260 may be referredto as forming a forward signal path of the encoder 20, whereas theinverse quantization unit 210, the inverse transform processing unit212, the reconstruction unit 214, the buffer 216, the loop filter 220,the decoded picture buffer (DPB) 230, the inter prediction unit 244 andthe intra-prediction unit 254 may be referred to as forming a backwardsignal path of the video encoder 20, wherein the backward signal path ofthe video encoder 20 corresponds to the signal path of the decoder (seevideo decoder 30 in FIG. 3). The inverse quantization unit 210, theinverse transform processing unit 212, the reconstruction unit 214, theloop filter 220, the decoded picture buffer (DPB) 230, the interprediction unit 244 and the intra-prediction unit 254 are also referredto forming the “built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive, e.g. via input 201, apicture 17 (or picture data 17), e.g. picture of a sequence of picturesforming a video or video sequence. The received picture or picture datamay also be a pre-processed picture 19 (or pre-processed picture data19). For sake of simplicity the following description refers to thepicture 17. The picture 17 may also be referred to as current picture orpicture to be coded (in particular in video coding to distinguish thecurrent picture from other pictures, e.g. previously encoded and/ordecoded pictures of the same video sequence, i.e. the video sequencewhich also comprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array ormatrix of samples with intensity values. A sample in the array may alsobe referred to as pixel (short form of picture element) or a pel. Thenumber of samples in horizontal and vertical direction (or axis) of thearray or picture define the size and/or resolution of the picture. Forrepresentation of color, typically three color components are employed,i.e. the picture may be represented or include three sample arrays. InRBG format or color space a picture comprises a corresponding red, greenand blue sample array. However, in video coding each pixel is typicallyrepresented in a luminance and chrominance format or color space, e.g.YCbCr, which comprises a luminance component indicated by Y (sometimesalso L is used instead) and two chrominance components indicated by Cband Cr. The luminance (or short luma) component Y represents thebrightness or grey level intensity (e.g. like in a grey-scale picture),while the two chrominance (or short chroma) components Cb and Crrepresent the chromaticity or color information components. Accordingly,a picture in YCbCr format comprises a luminance sample array ofluminance sample values (Y), and two chrominance sample arrays ofchrominance values (Cb and Cr). Pictures in RGB format may be convertedor transformed into YCbCr format and vice versa, the process is alsoknown as color transformation or conversion. If a picture is monochrome,the picture may comprise only a luminance sample array. Accordingly, apicture may be, for example, an array of luma samples in monochromeformat or an array of luma samples and two corresponding arrays ofchroma samples in 4:2:0, 4:2:2, and 4:4:4 colour format.

Embodiments of the video encoder 20 may comprise a picture partitioningunit (not depicted in FIG. 2) configured to partition the picture 17into a plurality of (typically non-overlapping) picture blocks 203.These blocks may also be referred to as root blocks, macro blocks(H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU)(H.265/HEVC and VVC). The picture partitioning unit may be configured touse the same block size for all pictures of a video sequence and thecorresponding grid defining the block size, or to change the block sizebetween pictures or subsets or groups of pictures, and partition eachpicture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receivedirectly a block 203 of the picture 17, e.g. one, several or all blocksforming the picture 17. The picture block 203 may also be referred to ascurrent picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or can be regardedas a two-dimensional array or matrix of samples with intensity values(sample values), although of smaller dimension than the picture 17. Inother words, the block 203 may comprise, e.g., one sample array (e.g. aluma array in case of a monochrome picture 17, or a luma or chroma arrayin case of a color picture) or three sample arrays (e.g. a luma and twochroma arrays in case of a color picture 17) or any other number and/orkind of arrays depending on the color format applied. The number ofsamples in horizontal and vertical direction (or axis) of the block 203define the size of block 203. Accordingly, a block may, for example, anM×N (M-column by N-row) array of samples, or an M×N array of transformcoefficients.

Embodiments of the video encoder 20 as shown in FIG. 2 may be configuredto encode the picture 17 block by block, e.g. the encoding andprediction is performed per block 203.

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using slices (alsoreferred to as video slices), wherein a picture may be partitioned intoor encoded using one or more slices (typically non-overlapping), andeach slice may comprise one or more blocks (e.g. CTUs).

Embodiments of the video encoder 20 as shown in FIG. 2 may be furtherconfigured to partition and/or encode the picture by using tile groups(also referred to as video tile groups) and/or tiles (also referred toas video tiles), wherein a picture may be partitioned into or encodedusing one or more tile groups (typically non-overlapping), and each tilegroup may comprise, e.g. one or more blocks (e.g. CTUs) or one or moretiles, wherein each tile, e.g. may be of rectangular shape and maycomprise one or more blocks (e.g. CTUs), e.g. complete or fractionalblocks.

Residual Calculation

The residual calculation unit 204 may be configured to calculate aresidual block 205 (also referred to as residual 205) based on thepicture block 203 and a prediction block 265 (further details about theprediction block 265 are provided later), e.g. by subtracting samplevalues of the prediction block 265 from sample values of the pictureblock 203, sample by sample (pixel by pixel) to obtain the residualblock 205 in the sample domain.

Transform

The transform processing unit 206 may be configured to apply atransform, e.g. a discrete cosine transform (DCT) or discrete sinetransform (DST), on the sample values of the residual block 205 toobtain transform coefficients 207 in a transform domain. The transformcoefficients 207 may also be referred to as transform residualcoefficients and represent the residual block 205 in the transformdomain.

The transform processing unit 206 may be configured to apply integerapproximations of DCT/DST, such as the transforms specified forH.265/HEVC. Compared to an orthogonal DCT transform, such integerapproximations are typically scaled by a certain factor. In order topreserve the norm of the residual block which is processed by forwardand inverse transforms, additional scaling factors are applied as partof the transform process. The scaling factors are typically chosen basedon certain constraints like scaling factors being a power of two forshift operations, bit depth of the transform coefficients, tradeoffbetween accuracy and implementation costs, etc. Specific scaling factorsare, for example, specified for the inverse transform, e.g. by inversetransform processing unit 212 (and the corresponding inverse transform,e.g. by inverse transform processing unit 312 at video decoder 30) andcorresponding scaling factors for the forward transform, e.g. bytransform processing unit 206, at an encoder 20 may be specifiedaccordingly.

Embodiments of the video encoder 20 (respectively transform processingunit 206) may be configured to output transform parameters, e.g. a typeof transform or transforms, e.g. directly or encoded or compressed viathe entropy encoding unit 270, so that, e.g., the video decoder 30 mayreceive and use the transform parameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transformcoefficients 207 to obtain quantized coefficients 209, e.g. by applyingscalar quantization or vector quantization. The quantized coefficients209 may also be referred to as quantized transform coefficients 209 orquantized residual coefficients 209.

The quantization process may reduce the bit depth associated with someor all of the transform coefficients 207. For example, an n-bittransform coefficient may be rounded down to an m-bit Transformcoefficient during quantization, where n is greater than m. The degreeof quantization may be modified by adjusting a quantization parameter(QP). For example for scalar quantization, different scaling may beapplied to achieve finer or coarser quantization. Smaller quantizationstep sizes correspond to finer quantization, whereas larger quantizationstep sizes correspond to coarser quantization. The applicablequantization step size may be indicated by a quantization parameter(QP). The quantization parameter may for example be an index to apredefined set of applicable quantization step sizes. For example, smallquantization parameters may correspond to fine quantization (smallquantization step sizes) and large quantization parameters maycorrespond to coarse quantization (large quantization step sizes) orvice versa. The quantization may include division by a quantization stepsize and a corresponding and/or the inverse dequantization, e.g. byinverse quantization unit 210, may include multiplication by thequantization step size. Embodiments according to some standards, e.g.HEVC, may be configured to use a quantization parameter to determine thequantization step size. Generally, the quantization step size may becalculated based on a quantization parameter using a fixed pointapproximation of an equation including division. Additional scalingfactors may be introduced for quantization and dequantization to restorethe norm of the residual block, which might get modified because of thescaling used in the fixed point approximation of the equation forquantization step size and quantization parameter. In one exampleimplementation, the scaling of the inverse transform and dequantizationmight be combined. Alternatively, customized quantization tables may beused and signaled from an encoder to a decoder, e.g. in a bitstream. Thequantization is a lossy operation, wherein the loss increases withincreasing quantization step sizes.

Embodiments of the video encoder 20 (respectively quantization unit 208)may be configured to output quantization parameters (QP), e.g. directlyor encoded via the entropy encoding unit 270, so that, e.g., the videodecoder 30 may receive and apply the quantization parameters fordecoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inversequantization of the quantization unit 208 on the quantized coefficientsto obtain dequantized coefficients 211, e.g. by applying the inverse ofthe quantization scheme applied by the quantization unit 208 based on orusing the same quantization step size as the quantization unit 208. Thedequantized coefficients 211 may also be referred to as dequantizedresidual coefficients 211 and correspond—although typically notidentical to the transform coefficients due to the loss byquantization—to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply theinverse transform of the transform applied by the transform processingunit 206, e.g. an inverse discrete cosine transform (DCT) or inversediscrete sine transform (DST) or other inverse transforms, to obtain areconstructed residual block 213 (or corresponding dequantizedcoefficients 213) in the sample domain. The reconstructed residual block213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g. adder or summer 214) is configured toadd the transform block 213 (i.e. reconstructed residual block 213) tothe prediction block 265 to obtain a reconstructed block 215 in thesample domain, e.g. by adding—sample by sample—the sample values of thereconstructed residual block 213 and the sample values of the predictionblock 265.

Filtering

The loop filter unit 220 (or short “loop filter” 220), is configured tofilter the reconstructed block 215 to obtain a filtered block 221, or ingeneral, to filter reconstructed samples to obtain filtered samples. Theloop filter unit is, e.g., configured to smooth pixel transitions, orotherwise improve the video quality. The loop filter unit 220 maycomprise one or more loop filters such as a de-blocking filter, asample-adaptive offset (SAO) filter or one or more other filters, e.g. abilateral filter, an adaptive loop filter (ALF), a sharpening, asmoothing filters or a collaborative filters, or any combinationthereof. Although the loop filter unit 220 is shown in FIG. 2 as beingan in loop filter, in other configurations, the loop filter unit 220 maybe implemented as a post loop filter. The filtered block 221 may also bereferred to as filtered reconstructed block 221.

Embodiments of the video encoder 20 (respectively loop filter unit 220)may be configured to output loop filter parameters (such as sampleadaptive offset information), e.g. directly or encoded via the entropyencoding unit 270, so that, e.g., a decoder 30 may receive and apply thesame loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that storesreference pictures, or in general reference picture data, for encodingvideo data by video encoder 20. The DPB 230 may be formed by any of avariety of memory devices, such as dynamic random access memory (DRAM),including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. The decodedpicture buffer (DPB) 230 may be configured to store one or more filteredblocks 221. The decoded picture buffer 230 may be further configured tostore other previously filtered blocks, e.g. previously reconstructedand filtered blocks 221, of the same current picture or of differentpictures, e.g. previously reconstructed pictures, and may providecomplete previously reconstructed, i.e. decoded, pictures (andcorresponding reference blocks and samples) and/or a partiallyreconstructed current picture (and corresponding reference blocks andsamples), for example for inter prediction. The decoded picture buffer(DPB) 230 may be also configured to store one or more unfilteredreconstructed blocks 215, or in general unfiltered reconstructedsamples, e.g. if the reconstructed block 215 is not filtered by loopfilter unit 220, or any other further processed version of thereconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262,inter-prediction unit 244 and intra-prediction unit 254, and isconfigured to receive or obtain original picture data, e.g. an originalblock 203 (current block 203 of the current picture 17), andreconstructed picture data, e.g. filtered and/or unfilteredreconstructed samples or blocks of the same (current) picture and/orfrom one or a plurality of previously decoded pictures, e.g. fromdecoded picture buffer 230 or other buffers (e.g. line buffer, notshown). The reconstructed picture data is used as reference picture datafor prediction, e.g. inter-prediction or intra-prediction, to obtain aprediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select apartitioning for a current block prediction mode (including nopartitioning) and a prediction mode (e.g. an intra or inter predictionmode) and generate a corresponding prediction block 265, which is usedfor the calculation of the residual block 205 and for the reconstructionof the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to selectthe partitioning and the prediction mode (e.g. from those supported byor available for mode selection unit 260), which provide the best matchor in other words the minimum residual (minimum residual means bettercompression for transmission or storage), or a minimum signalingoverhead (minimum signaling overhead means better compression fortransmission or storage), or which considers or balances both. The modeselection unit 260 may be configured to determine the partitioning andprediction mode based on rate distortion optimization (RDO), i.e. selectthe prediction mode which provides a minimum rate distortion. Terms like“best”, “minimum”, “optimum” etc. in this context do not necessarilyrefer to an overall “best”, “minimum”, “optimum”, etc. but may alsorefer to the fulfillment of a termination or selection criterion like avalue exceeding or falling below a threshold or other constraintsleading potentially to a “sub-optimum selection” but reducing complexityand processing time.

In other words, the partitioning unit 262 may be configured to partitionthe block 203 into smaller block partitions or sub-blocks (which formagain blocks), e.g. iteratively using quad-tree-partitioning (QT),binary partitioning (BT) or triple-tree-partitioning (TT) or anycombination thereof, and to perform, e.g., the prediction for each ofthe block partitions or sub-blocks, wherein the mode selection comprisesthe selection of the tree-structure of the partitioned block 203 and theprediction modes are applied to each of the block partitions orsub-blocks.

In the following the partitioning (e.g. by partitioning unit 260) andprediction processing (by inter-prediction unit 244 and intra-predictionunit 254) performed by an example video encoder 20 will be explained inmore detail.

Partitioning

The partitioning unit 262 may partition (or split) a current block 203into smaller partitions, e.g. smaller blocks of square or rectangularsize. These smaller blocks (which may also be referred to as sub-blocks)may be further partitioned into even smaller partitions. This is alsoreferred to tree-partitioning or hierarchical tree-partitioning, whereina root block, e.g. at root tree-level 0 (hierarchy-level 0, depth 0),may be recursively partitioned, e.g. partitioned into two or more blocksof a next lower tree-level, e.g. nodes at tree-level 1 (hierarchy-level1, depth 1), wherein these blocks may be again partitioned into two ormore blocks of a next lower level, e.g. tree-level 2 (hierarchy-level 2,depth 2), etc. until the partitioning is terminated, e.g. because atermination criterion is fulfilled, e.g. a maximum tree depth or minimumblock size is reached. Blocks which are not further partitioned are alsoreferred to as leaf-blocks or leaf nodes of the tree. A tree usingpartitioning into two partitions is referred to as binary-tree (BT), atree using partitioning into three partitions is referred to asternary-tree (TT), and a tree using partitioning into four partitions isreferred to as quad-tree (QT).

As mentioned before, the term “block” as used herein may be a portion,in particular a square or rectangular portion, of a picture. Withreference, for example, to HEVC and VVC, the block may be or correspondto a coding tree unit (CTU), a coding unit (CU), prediction unit (PU),and transform unit (TU) and/or to the corresponding blocks, e.g. acoding tree block (CTB), a coding block (CB), a transform block (TB) orprediction block (PB).

For example, a coding tree unit (CTU) may be or comprise a CTB of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate colour planes and syntaxstructures used to code the samples. Correspondingly, a coding treeblock (CTB) may be an N×N block of samples for some value of N such thatthe division of a component into CTBs is a partitioning. A coding unit(CU) may be or comprise a coding block of luma samples, twocorresponding coding blocks of chroma samples of a picture that hasthree sample arrays, or a coding block of samples of a monochromepicture or a picture that is coded using three separate colour planesand syntax structures used to code the samples. Correspondingly a codingblock (CB) may be an M×N block of samples for some values of M and Nsuch that the division of a CTB into coding blocks is a partitioning.

In embodiments, e.g., according to HEVC, a coding tree unit (CTU) may besplit into CUs by using a quad-tree structure denoted as coding tree.The decision whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction is made at the CUlevel. Each CU can be further split into one, two or four PUs accordingto the PU splitting type. Inside one PU, the same prediction process isapplied and the relevant information is transmitted to the decoder on aPU basis. After obtaining the residual block by applying the predictionprocess based on the PU splitting type, a CU can be partitioned intotransform units (TUs) according to another quadtree structure similar tothe coding tree for the CU.

In embodiments, e.g., according to the latest video coding standardcurrently in development, which is referred to as Versatile Video Coding(VVC), a combined Quad-tree and binary tree (QTBT) partitioning is forexample used to partition a coding block. In the QTBT block structure, aCU can have either a square or rectangular shape. For example, a codingtree unit (CTU) is first partitioned by a quadtree structure. Thequadtree leaf nodes are further partitioned by a binary tree or ternary(or triple) tree structure. The partitioning tree leaf nodes are calledcoding units (CUs), and that segmentation is used for prediction andtransform processing without any further partitioning. This means thatthe CU, PU and TU have the same block size in the QTBT coding blockstructure. In parallel, multiple partition, for example, triple treepartition may be used together with the QTBT block structure.

In one example, the mode selection unit 260 of video encoder 20 may beconfigured to perform any combination of the partitioning techniquesdescribed herein.

As described above, the video encoder 20 is configured to determine orselect the best or an optimum prediction mode from a set of (e.g.pre-determined) prediction modes. The set of prediction modes maycomprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 differentintra-prediction modes, e.g. non-directional modes like DC (or mean)mode and planar mode, or directional modes, e.g. as defined in HEVC, ormay comprise 67 different intra-prediction modes, e.g. non-directionalmodes like DC (or mean) mode and planar mode, or directional modes, e.g.as defined for VVC.

The intra-prediction unit 254 is configured to use reconstructed samplesof neighboring blocks of the same current picture to generate anintra-prediction block 265 according to an intra-prediction mode of theset of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit260) is further configured to output intra-prediction parameters (or ingeneral information indicative of the selected intra prediction mode forthe block) to the entropy encoding unit 270 in form of syntax elements266 for inclusion into the encoded picture data 21, so that, e.g., thevideo decoder 30 may receive and use the prediction parameters fordecoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the availablereference pictures (i.e. previous at least partially decoded pictures,e.g. stored in DPB 230) and other inter-prediction parameters, e.g.whether the whole reference picture or only a part, e.g. a search windowarea around the area of the current block, of the reference picture isused for searching for a best matching reference block, and/or e.g.whether pixel interpolation is applied, e.g. half/semi-pel and/orquarter-pel interpolation, or not.

Additional to the above prediction modes, skip mode and/or direct modemay be applied.

The inter prediction unit 244 may include a motion estimation (ME) unitand a motion compensation (MC) unit (both not shown in FIG. 2). Themotion estimation unit may be configured to receive or obtain thepicture block 203 (current picture block 203 of the current picture 17)and a decoded picture 231, or at least one or a plurality of previouslyreconstructed blocks, e.g. reconstructed blocks of one or a plurality ofother/different previously decoded pictures 231, for motion estimation.E.g. a video sequence may comprise the current picture and thepreviously decoded pictures 231, or in other words, the current pictureand the previously decoded pictures 231 may be part of or form asequence of pictures forming a video sequence.

The encoder 20 may, e.g., be configured to select a reference block froma plurality of reference blocks of the same or different pictures of theplurality of other pictures and provide a reference picture (orreference picture index) and/or an offset (spatial offset) between theposition (x, y coordinates) of the reference block and the position ofthe current block as inter prediction parameters to the motionestimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain, e.g. receive, aninter prediction parameter and to perform inter prediction based on orusing the inter prediction parameter to obtain an inter prediction block265. Motion compensation, performed by the motion compensation unit, mayinvolve fetching or generating the prediction block based on themotion/block vector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Interpolation filtering maygenerate additional pixel samples from known pixel samples, thuspotentially increasing the number of candidate prediction blocks thatmay be used to code a picture block. Upon receiving the motion vectorfor the PU of the current picture block, the motion compensation unitmay locate the prediction block to which the motion vector points in oneof the reference picture lists.

The motion compensation unit may also generate syntax elementsassociated with the blocks and video slices for use by video decoder 30in decoding the picture blocks of the video slice. In addition or as analternative to slices and respective syntax elements, tile groups and/ortiles and respective syntax elements may be generated or used.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, anentropy encoding algorithm or scheme (e.g. a variable length coding(VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmeticcoding scheme, a binarization, a context adaptive binary arithmeticcoding (CABAC), syntax-based context-adaptive binary arithmetic coding(SBAC), probability interval partitioning entropy (PIPE) coding oranother entropy encoding methodology or technique) or bypass (nocompression) on the quantized coefficients 209, inter predictionparameters, intra prediction parameters, loop filter parameters and/orother syntax elements to obtain encoded picture data 21 which can beoutput via the output 272, e.g. in the form of an encoded bitstream 21,so that, e.g., the video decoder 30 may receive and use the parametersfor decoding, . The encoded bitstream 21 may be transmitted to videodecoder 30, or stored in a memory for later transmission or retrieval byvideo decoder 30.

Other structural variations of the video encoder 20 can be used toencode the video stream. For example, a non-transform based encoder 20can quantize the residual signal directly without the transformprocessing unit 206 for certain blocks or frames. In anotherimplementation, an encoder 20 can have the quantization unit 208 and theinverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

FIG. 3 shows an example of a video decoder 30 that is configured toimplement the techniques of this present application. The video decoder30 is configured to receive encoded picture data 21 (e.g. encodedbitstream 21), e.g. encoded by encoder 20, to obtain a decoded picture331. The encoded picture data or bitstream comprises information fordecoding the encoded picture data, e.g. data that represents pictureblocks of an encoded video slice (and/or tile groups or tiles) andassociated syntax elements.

In the example of FIG. 3, the decoder 30 comprises an entropy decodingunit 304, an inverse quantization unit 310, an inverse transformprocessing unit 312, a reconstruction unit 314 (e.g. a summer 314), aloop filter 320, a decoded picture buffer (DPB) 330, a mode applicationunit 360, an inter prediction unit 344 and an intra prediction unit 354.Inter prediction unit 344 may be or include a motion compensation unit.Video decoder 30 may, in some examples, perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 100 from FIG. 2.

As explained with regard to the encoder 20, the inverse quantizationunit 210, the inverse transform processing unit 212, the reconstructionunit 214 the loop filter 220, the decoded picture buffer (DPB) 230, theinter prediction unit 344 and the intra prediction unit 354 are alsoreferred to as forming the “built-in decoder” of video encoder 20.Accordingly, the inverse quantization unit 310 may be identical infunction to the inverse quantization unit 110, the inverse transformprocessing unit 312 may be identical in function to the inversetransform processing unit 212, the reconstruction unit 314 may beidentical in function to reconstruction unit 214, the loop filter 320may be identical in function to the loop filter 220, and the decodedpicture buffer 330 may be identical in function to the decoded picturebuffer 230. Therefore, the explanations provided for the respectiveunits and functions of the video 20 encoder apply correspondingly to therespective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21(or in general encoded picture data 21) and perform, for example,entropy decoding to the encoded picture data 21 to obtain, e.g.,quantized coefficients 309 and/or decoded coding parameters (not shownin FIG. 3), e.g. any or all of inter prediction parameters (e.g.reference picture index and motion vector), intra prediction parameter(e.g. intra prediction mode or index), transform parameters,quantization parameters, loop filter parameters, and/or other syntaxelements. Entropy decoding unit 304 maybe configured to apply thedecoding algorithms or schemes corresponding to the encoding schemes asdescribed with regard to the entropy encoding unit 270 of the encoder20. Entropy decoding unit 304 may be further configured to provide interprediction parameters, intra prediction parameter and/or other syntaxelements to the mode application unit 360 and other parameters to otherunits of the decoder 30. Video decoder 30 may receive the syntaxelements at the video slice level and/or the video block level. Inaddition or as an alternative to slices and respective syntax elements,tile groups and/or tiles and respective syntax elements may be receivedand/or used.

Inverse Quantization

The inverse quantization unit 310 may be configured to receivequantization parameters (QP) (or in general information related to theinverse quantization) and quantized coefficients from the encodedpicture data 21 (e.g. by parsing and/or decoding, e.g. by entropydecoding unit 304) and to apply based on the quantization parameters aninverse quantization on the decoded quantized coefficients 309 to obtaindequantized coefficients 311, which may also be referred to as transformcoefficients 311. The inverse quantization process may include use of aquantization parameter determined by video encoder 20 for each videoblock in the video slice (or tile or tile group) to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receivedequantized coefficients 311, also referred to as transform coefficients311, and to apply a transform to the dequantized coefficients 311 inorder to obtain reconstructed residual blocks 213 in the sample domain.The reconstructed residual blocks 213 may also be referred to astransform blocks 313. The transform may be an inverse transform, e.g.,an inverse DCT, an inverse DST, an inverse integer transform, or aconceptually similar inverse transform process. The inverse transformprocessing unit 312 may be further configured to receive transformparameters or corresponding information from the encoded picture data 21(e.g. by parsing and/or decoding, e.g. by entropy decoding unit 304) todetermine the transform to be applied to the dequantized coefficients311.

Reconstruction

The reconstruction unit 314 (e.g. adder or summer 314) may be configuredto add the reconstructed residual block 313, to the prediction block 365to obtain a reconstructed block 315 in the sample domain, e.g. by addingthe sample values of the reconstructed residual block 313 and the samplevalues of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the codingloop) is configured to filter the reconstructed block 315 to obtain afiltered block 321, e.g. to smooth pixel transitions, or otherwiseimprove the video quality. The loop filter unit 320 may comprise one ormore loop filters such as a de-blocking filter, a sample-adaptive offset(SAO) filter or one or more other filters, e.g. a bilateral filter, anadaptive loop filter (ALF), a sharpening, a smoothing filters or acollaborative filters, or any combination thereof. Although the loopfilter unit 320 is shown in FIG. 3 as being an in loop filter, in otherconfigurations, the loop filter unit 320 may be implemented as a postloop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decodedpicture buffer 330, which stores the decoded pictures 331 as referencepictures for subsequent motion compensation for other pictures and/orfor output respectively display.

The decoder 30 is configured to output the decoded picture 311, e.g. viaoutput 312, for presentation or viewing to a user.

Prediction

The inter prediction unit 344 may be identical to the inter predictionunit 244 (in particular to the motion compensation unit) and the intraprediction unit 354 may be identical to the inter prediction unit 254 infunction, and performs split or partitioning decisions and predictionbased on the partitioning and/or prediction parameters or respectiveinformation received from the encoded picture data 21 (e.g. by parsingand/or decoding, e.g. by entropy decoding unit 304). Mode applicationunit 360 may be configured to perform the prediction (intra or interprediction) per block based on reconstructed pictures, blocks orrespective samples (filtered or unfiltered) to obtain the predictionblock 365.

When the video slice is coded as an intra coded (I) slice, intraprediction unit 354 of mode application unit 360 is configured togenerate prediction block 365 for a picture block of the current videoslice based on a signaled intra prediction mode and data from previouslydecoded blocks of the current picture. When the video picture is codedas an inter coded (i.e., B, or P) slice, inter prediction unit 344 (e.g.motion compensation unit) of mode application unit 360 is configured toproduce prediction blocks 365 for a video block of the current videoslice based on the motion vectors and other syntax elements receivedfrom entropy decoding unit 304. For inter prediction, the predictionblocks may be produced from one of the reference pictures within one ofthe reference picture lists. Video decoder 30 may construct thereference frame lists, List 0 and List 1, using default constructiontechniques based on reference pictures stored in DPB 330. The same orsimilar may be applied for by embodiments using tile groups (e.g. videotile groups) and/or tiles (e.g. video tiles) in addition oralternatively to slices (e.g. video slices), e.g. a video may be codedusing I, P or B tile groups and/or tiles.

Mode application unit 360 is configured to determine the predictioninformation for a video block of the current video slice by parsing themotion vectors or related information and other syntax elements, anduses the prediction information to produce the prediction blocks for thecurrent video block being decoded. For example, the mode applicationunit 360 uses some of the received syntax elements to determine aprediction mode (e.g., intra or inter prediction) used to code the videoblocks of the video slice, an inter prediction slice type (e.g., Bslice, P slice, or GPB slice), construction information for one or moreof the reference picture lists for the slice, motion vectors for eachinter encoded video block of the slice, inter prediction status for eachinter coded video block of the slice, and other information to decodethe video blocks in the current video slice. The same or similar may beapplied for by embodiments using tile groups (e.g. video tile groups)and/or tiles (e.g. video tiles) in addition or alternatively to slices(e.g. video slices), e.g. a video may be coded using I, P or B tilegroups and/or tiles.

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using slices (also referred toas video slices), wherein a picture may be partitioned into or decodedusing one or more slices (typically non-overlapping), and each slice maycomprise one or more blocks (e.g. CTUs).

Embodiments of the video decoder 30 as shown in FIG. 3 may be configuredto partition and/or decode the picture by using tile groups (alsoreferred to as video tile groups) and/or tiles (also referred to asvideo tiles), wherein a picture may be partitioned into or decoded usingone or more tile groups (typically non-overlapping), and each tile groupmay comprise, e.g. one or more blocks (e.g. CTUs) or one or more tiles,wherein each tile, e.g. may be of rectangular shape and may comprise oneor more blocks (e.g. CTUs), e.g. complete or fractional blocks.

Other variations of the video decoder 30 can be used to decode theencoded picture data 21. For example, the decoder 30 can produce theoutput video stream without the loop filtering unit 320. For example, anon-transform based decoder 30 can inverse-quantize the residual signaldirectly without the inverse-transform processing unit 312 for certainblocks or frames. In another implementation, the video decoder 30 canhave the inverse-quantization unit 310 and the inverse-transformprocessing unit 312 combined into a single unit.

It should be understood that, in the encoder 20 and the decoder 30, aprocessing result of a current operation may be further processed andthen output to the next operation. For example, after interpolationfiltering, motion vector derivation or loop filtering, a furtheroperation, such as Clip or shift, may be performed on the processingresult of the interpolation filtering, motion vector derivation or loopfiltering.

It should be noted that further operations may be applied to the derivedmotion vectors of current block (including but not limit to controlpoint motion vectors of affine mode, sub-block motion vectors in affine,planar, ATMVP modes, temporal motion vectors, and so on). For example,the value of motion vector is constrained to a predefined rangeaccording to its representing bit. If the representing bit of motionvector is bitDepth, then the range is −2{circumflex over( )}(bitDepth-1)˜2{circumflex over ( )}(bitDepth-1)-1, where“{circumflex over ( )}” means exponentiation. For example, if bitDepthis set equal to 16, the range is −32768˜32767; if bitDepth is set equalto 18, the range is −131072˜131071. For example, the value of thederived motion vector (e.g. the MVs of four 4×4 sub-blocks within one8×8 block) is constrained such that the max difference between integerparts of the four 4×4 sub-block MVs is no more than N pixels, such as nomore than 1 pixel. Here provides two methods for constraining the motionvector according to the bitDepth.

Method 1: remove the overflow MSB (most significant bit) by flowingoperations

ux=(mvx+2^(bitDepth))% 2^(bitDepth)  (1)

mvx=(ux>=2^(bitDepth-1))?(ux−2^(bitDepth)):ux  (2)

uy=(mvy+2^(bitDepth))% 2^(bitDepth)  (3)

mvy=(uy>=2^(bitDepth-1))?(uy−2^(bitDepth)):uy  (4)

where mvx is a horizontal component of a motion vector of an image blockor a sub-block, mvy is a vertical component of a motion vector of animage block or a sub-block, and ux and uy indicates an intermediatevalue;

For example, if the value of mvx is −32769, after applying formula (1)and (2), the resulting value is 32767. In computer system, decimalnumbers are stored as two's complement. The two's complement of −32769is 1,0111,1111,1111,1111 (17 bits), then the MSB is discarded, so theresulting two's complement is 0111,1111,1111,1111 (decimal number is32767), which is same as the output by applying formula (1) and (2).

ux=(mvpx+mvdx+2^(bitDepth))% 2^(bitDepth)  (5)

mvx=(ux>=2^(bitDepth-1))?(ux−2^(bitDepth)):ux  (6)

uy=(mvpy+mvdy+2^(bitDepth))% 2^(bitDepth)  (7)

mvy=(uy>=2^(bitDepth-1))?(uy−2^(bitDepth)):uy  (8)

The operations may be applied during the sum of mvp and mvd, as shown informula (5) to (8).

Method 2: remove the overflow MSB by clipping the value

vx=Clip3(−2^(bitDept-1), 2^(bitDepth-1)−1, vx)

vy=Clip3(−2^(bitDepth-1), 2^(bitDepth-1)−1, vy)

where vx is a horizontal component of a motion vector of an image blockor a sub-block, vy is a vertical component of a motion vector of animage block or a sub-block; x, y and z respectively correspond to threeinput value of the MV clipping process, and the definition of functionClip3 is as follow:

${{Clip}3\left( {x,y,z} \right)} = \left\{ \begin{matrix}x & ; & {z < x} \\y & ; & {z > y} \\z & ; & {otherwise}\end{matrix} \right.$

FIG. 4 is a schematic diagram of a video coding device 400 according toan embodiment of the disclosure. The video coding device 400 is suitablefor implementing the disclosed embodiments as described herein. In anembodiment, the video coding device 400 may be a decoder such as videodecoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.

The video coding device 400 comprises ingress ports 410 (or input ports410) and receiver units (Rx) 420 for receiving data; a processor, logicunit, or central processing unit (CPU) 430 to process the data;transmitter units (Tx) 440 and egress ports 450 (or output ports 450)for transmitting the data; and a memory 460 for storing the data. Thevideo coding device 400 may also comprise optical-to-electrical (OE)components and electrical-to-optical (EO) components coupled to theingress ports 410, the receiver units 420, the transmitter units 440,and the egress ports 450 for egress or ingress of optical or electricalsignals.

The processor 430 is implemented by hardware and software. The processor430 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), FPGAs, ASICs, and DSPs. The processor 430 is incommunication with the ingress ports 410, receiver units 420,transmitter units 440, egress ports 450, and memory 460. The processor430 comprises a coding module 470. The coding module 470 implements thedisclosed embodiments described above. For instance, the coding module470 implements, processes, prepares, or provides the various codingoperations. The inclusion of the coding module 470 therefore provides asubstantial improvement to the functionality of the video coding device400 and effects a transformation of the video coding device 400 to adifferent state. Alternatively, the coding module 470 is implemented asinstructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, andsolid-state drives and may be used as an over-flow data storage device,to store programs when such programs are selected for execution, and tostore instructions and data that are read during program execution. Thememory 460 may be, for example, volatile and/or non-volatile and may bea read-only memory (ROM), random access memory (RAM), ternarycontent-addressable memory (TCAM), and/or static random-access memory(SRAM).

FIG. 5 is a simplified block diagram of an apparatus 500 that may beused as either or both of the source device 12 and the destinationdevice 14 from FIG. 1 according to an exemplary embodiment.

A processor 502 in the apparatus 500 can be a central processing unit.Alternatively, the processor 502 can be any other type of device, ormultiple devices, capable of manipulating or processing informationnow-existing or hereafter developed. Although the disclosedimplementations can be practiced with a single processor as shown, e.g.,the processor 502, advantages in speed and efficiency can be achievedusing more than one processor.

A memory 504 in the apparatus 500 can be a read only memory (ROM) deviceor a random access memory (RAM) device in an implementation. Any othersuitable type of storage device can be used as the memory 504. Thememory 504 can include code and data 506 that is accessed by theprocessor 502 using a bus 512. The memory 504 can further include anoperating system 508 and application programs 510, the applicationprograms 510 including at least one program that permits the processor502 to perform the methods described here. For example, the applicationprograms 510 can include applications 1 through N, which further includea video coding application that performs the methods described here.

The apparatus 500 can also include one or more output devices, such as adisplay 518. The display 518 may be, in one example, a touch sensitivedisplay that combines a display with a touch sensitive element that isoperable to sense touch inputs. The display 518 can be coupled to theprocessor 502 via the bus 512.

Although depicted here as a single bus, the bus 512 of the apparatus 500can be composed of multiple buses. Further, the secondary storage 514can be directly coupled to the other components of the apparatus 500 orcan be accessed via a network and can comprise a single integrated unitsuch as a memory card or multiple units such as multiple memory cards.The apparatus 500 can thus be implemented in a wide variety ofconfigurations.

Background refer to Chroma intra prediction mode.

MIP (Matrix-based Intra Prediction) and IBC (Intra Block Copy) are twoprediction methods. MIP performs intra prediction based on pre-definedcoefficients. In IBC, sample values are predicted from other samples inthe same picture by means of a displacement vector called a blockvector, in a manner conceptually similar to motion-compensatedprediction.

Palette mode is a coding tool for screen content coding (SCC) to improvethe coding efficiency for screen contents such as computer generatedvideo with substantial amount of text and graphics. In the palette mode,pixels in a coding unit (CU) are represented by selected representativecolors according to the characteristics of screen contents in whichpixel values usually concentrate on few color values.

In some examples, MIP (or IBC, or Palette) mode are applied for the lumacomponent. When perform chroma intra prediction mode derivation using DMmode (derive mode from corresponding luma component), special modes areassigned for the DM mode (lumaIntraPredMode) if the corresponding lumablock is applied with MIP or IBC, or Palette mode.

There are many documents refers to Chroma intra prediction modederivation process, for example, ITU JVET-00925 discloses set Chromaderive mode, DM, as Planar mode if Matrix-based Intra Prediction, MIP,is enabled, ITU JVET-00258 discloses disable Intra Block Copy, IBC, forChroma component, ITU JVET-O0651 discloses set Chroma DM mode as DC ifIBC is enabled.

In an example, a process for the chroma derivation is as follows:

Input to this process are:

-   a luma location (xCb, yCb) specifying the top-left sample of the    current chroma coding block relative to the top-left luma sample of    the current picture,-   a variable cbWidth specifying the width of the current coding block    in luma samples,-   a variable cbHeight specifying the height of the current coding    block in luma samples.

In this process, the chroma intra prediction modeIntraPredModeC[xCb][yCb] is derived.

The corresponding luma intra prediction mode lumaIntraPredMode isderived as follows:

-   If intra_mip_flag[xCb][yCb] is equal to 1, lumaIntraPredMode is set    equal to INTRA_PLANAR.-   Otherwise if CuPredMode[xCb][yCb] is equal to MODE_IBC,    lumaIntraPredMode is set equal to INTRA_DC.-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

Among the above process, intra_mip_flag[xCb][yCb] equals to 1 specifiesthat the intra prediction type for luma samples is matrix-based intraprediction, and intra_mip_flag[xCb][yCb] equals to 0 specifies that theintra prediction type for luma samples is not matrix-based intraprediction.

CuPredMode[xCb][yCb] equal to MODE_IBC specifies that the currentprediction block is applied with IBC mode.

IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] specifies the luma intraprediction mode for the prediction block including the position of(xCb+cbWidth/2, yCb+cbHeight/2), i.e. the ‘middle’ of the correspondingluma prediction block.

In an example, the chroma intra prediction mode IntraPredModeC[xCb][yCb]is derived using intra_chroma_pred_mode[xCb][yCb] and lumaIntraPredModeas showed in Table 8-5 or Table 8-6, there are also many other examplesor tables may be used to derive the chroma intra prediction modeIntraPredModeC[xCb][yCb]. Among the above process,

intra_chroma_pred_mode[x0][y0] specifies the intra prediction mode(index) for chroma samples. Note, it is not the final intra predictionmode, it would be more appropriate to consider this value as anintermediate index, as the input to obtain the final intra predictionmode for chroma samples.

TABLE 8-5 Specification of IntraPredModeC[xCb][yCb] depending onintra_chroma_pred_mode[xCb][yCb] and lumaIntraPredMode when a value ofsps_cclm_enabled_flag is equal to 0. lumaIntraPredMode Xintra_chroma_pred_mode[xCb][yCb] 0 50 18 1 (0 <= X <= 66) 0 66 0 0 0 0 150 66 50 50 50 2 18 18 66 18 18 3 1 1 1 66 1 4 0 50 18 1 X

TABLE 8-6 Specification of IntraPredModeC[xCb][yCb] depending onintra_chroma_pred_mode[xCb][yCb] and lumaIntraPredMode when a value ofsps_cclm_enabled_flag is equal to 1. lumaIntraPredMode Xintra_chroma_pred_mode[xCb][yCb] 0 50 18 1 (0 <= X <= 66) 0 66 0 0 0 0 150 66 50 50 50 2 18 18 66 18 18 3 1 1 1 66 1 4 81 81 81 81 81 5 82 82 8282 82 6 83 83 83 83 83 7 0 50 18 1 X

In above Table 8-5 and 8-6, sps_cclm_enabled_flag equal to 0 specifiesthat the Cross-Component Linear Model (CCLM) intra prediction from lumacomponent to chroma component is disabled. sps_cclm_enabled_flag equalto 1 specifies that the cross-component linear model intra predictionfrom luma component to chroma component is enabled.

In the example disclosed in the above process, a luma intra predictionmode (lumaIntraPredMode) is obtained, and then a chroma intra predictionmode (intra_chroma_pred_mode) is obtained, for example, from abitstream. According to the value of the luma intra prediction mode(lumaIntraPredMode) and the value of syntax intra_chroma_pred_mode, theoutput prediction mode is derived according to Table 8-5 and 8-6.

In some examples, according to table 8-5 and table 8-6, the output modemay be one of 70 modes. The 70 modes may be classified into 67 normalmodes and three Cross-component linear model (CCLM) modes. The 67 normalmodes may be further divided into non-angular modes (planar and DCmodes) and 65 angular modes (mode 2 to 66), as shown in FIG. 6. Modes81, 82, 83 corresponds to three CCLM (Cross-component linear model)modes, which corresponds to linear mode left and top (INTRA_LT_CCLM),linear mode left (INTRA_L_CCLM), and linear mode top (INTRA_T_CCLM).These modes are summarized in Table 8-3.

TABLE 8-3 Specification of intra prediction mode and associated namesIntra prediction mode Associated name 0 INTRA_PLANAR 1 INTRA_DC  2 . . .66 INTRA_ANGULAR2 . . . INTRA_ANGULAR66 81 . . . 83 INTRA_LT_CCLM,INTRA_L_CCLM, INTRA_T_CCLM

A misalignment between MIP (or IBC) flag's position and luma intraprediction mode's position can cause a potential problem in chroma intraprediction mode derivation.

Namely, the flag of intra_mip_flag (or CuPredMode) is fetched from theluma position (xCb, yCb), while the intra prediction mode of the lumablock is fetched from the position (xCb+cbWidth/2, yCb+cbHeight/2), asfollows (defined as VVC process of chroma intra prediction modederivation).

-   If a value of intra_mip_flag[xCb][yCb] is equal to 1,    lumaIntraPredMode is set equal to INTRA_PLANAR.-   Otherwise if CuPredMode[xCb][yCb] is equal to MODE_IBC,    lumaIntraPredMode is set equal to INTRA_DC-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

When CUPredMode[xCb][yCb] is equal to MODE_IBC, no intra prediction modeis defined in the working draft of VVC.

In an example as showed in FIG. 7, the partition of a luma predictionblock and a chroma prediction block in a coding area (for example, thecoding area is a CTU) is not aligned when dual-tree coding method isenabled (one tree partition for luma and one tree partition for chroma).For the sake of simplicity, it is assumed the chroma component in a CTUis partitioned into two parts, with left and right sub-partitions (leftCTU in FIG. 7). The luma component in a CTU is also partitioned into twoparts, however with top and bottom sub-partitions. The luma component'stop sub-partition is applied with normal intra prediction mode, and thebottom sub-partition is applied with the IBC mode (right CTU in FIG. 7).

In this example showed in FIG. 7, the chroma component is performingchroma intra prediction mode derivation. According to the VVC process ofchroma intra prediction mode derivation as defined before, a value ofintra_mip_flag[xCb][yCb] is equal to 0, since normal intra predictionmode is applied for the top sub-partition within the luma component,whose left-top position is (xCb, yCb). For the same reason,CuPredMode[xCb][yCb] is also not equal to MODE_IBC, where the position(xCb, yCb) belongs to the top sub-partition of the luma component andthere the block is applied with normal intra prediction. Therefore, thechroma intra prediction mode derivation will fetch the value of normalluma intra prediction mode at (xCb+cbWidth/2, yCb+cbHeight/2) (i.e.IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2]). However, the position(xCb+cbWidth/2, yCb+cbHeight/2) now point to a location in the bottomsub-partition in the luma component (as shown in the bottom CTU in FIG.7). The bottom sub-partition of luma component is applied with IBC andno luma intra prediction mode is defined. Therefore, the value ofIntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2] is an undefined value inthe current specification. In this corner case, the chroma intraprediction mode derivation process is broken.

The example raised in FIG. 7 shows a corner case where twosub-partitions in the luma component are applied with normal intraprediction mode and IBC mode, respectively. It can be deduced that thechroma derivation process is also broken when IBC is replaced by MIP orpalette mode.

A luma location (xCb, yCb) specifying the top-left sample of the currentchroma coding block, relative to the top-left luma sample of the currentpicture.

A luma location value (xCb, yCb) for the top-left location of Chromacomponent of a current coding block is obtained, the luma location value(xCb, yCb) is specified in luma sample of the current coding block; avalue of a first indication information (e.g. intra_mip_flag) for thecurrent coding block is obtained, the value of the first indicationinformation for the current coding block is derived corresponding to aluma position (cbWidth/2, cbHeight/2), relative to the top-left lumasample of the current coding block, cbWidth represents a width of thecurrent coding block in luma samples, cbHeight represents a height ofthe current coding block in luma samples (in an example, the firstindication information is derived from a luma location (xCb+cbWidth/2,yCb+cbHeight/2)).

As an example showed in FIG. 8, a location value for the top-leftposition of a current picture is (0, 0), and a location value for thetop-left position of a current coding block is (128, 64). The width ofthe current coding block is 64, the height of the current coding blockis 32. Hence, the location value which is used to derive intraprediction mode is ((128+64/2), 64+32/2)), i.e., (160, 80).

In one embodiment of the present disclosure, a position of IBC or MIPflags are aligned with the position of the luma intra prediction mode,the following process applies:

-   If a value of intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2] is equal    to 1, lumaIntraPredMode is set equal to INTRA_PLANAR.-   Otherwise if CuPredMode[xCb+cbWidth/2][yCb+cbHeight/2] is equal to    MODE_IBC, lumaIntraPredMode is set equal to INTRA_DC-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

In such case, taking FIG. 7 as an example again, the chroma intraprediction mode derivation would fall into the second branch (i.e.Otherwise if CuPredMode[xCb+cbWidth/2][yCb+cbHeight/2] is equal toMODE_IBC), the lumaIntraPredMode is set to equal to DC mode.

The method assures that IBC and MIP modes are detected in the firstplace using the aligned position, and thus the variablelumaIntraPredMode would be always assigned with valid luma intraprediction mode.

In one embodiment, the position of IBC or MIP flags are aligned with theposition of the luma intra prediction mode, and their correspondingintra prediction mode are both set to planar mode, the following processapplies:

-   If a value of an intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2] is    equal to 1, or CuPredMode[xCb+cbWidth/2][yCb+cbHeight/2] is equal to    MODE_IBC, lumaIntraPredMode is set equal to INTRA_PLANAR.-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

In one embodiment, the position of IBC or MIP flags are aligned with theposition of the luma intra prediction mode, and their correspondingintra prediction mode are both set to DC mode, the following processapplies:

-   If a value of an intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2] is    equal to 1, or CuPredMode[xCb+cbWidth/2][yCb+cbHeight/2] is equal to    MODE_IBC, lumaIntraPredMode is set equal to INTRA_DC.-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

In one embodiment of the present disclosure, a position of IBC or MIPflags are aligned with the position of the luma intra prediction mode,the following process applies:

-   If a value of intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2] is equal    to 1, lumaIntraPredMode is set equal to INTRA_PLANAR.-   Otherwise if CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2] is equal    to MODE_IBC, lumaIntraPredMode is set equal to INTRA_DC-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

In one embodiment of the present disclosure, a position of IBC or MIP orpalette flags are aligned with the position of the luma intra predictionmode, the following process applies:

-   If a value of intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2] is equal    to 1, lumaIntraPredMode is set equal to INTRA_PLANAR.-   Otherwise if CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2] is equal    to MODE_IBC or MODE_PLT, lumaIntraPredMode is set equal to INTRA_DC-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

In one embodiment of the present disclosure, a position of IBC or MIP orpalette flags are aligned with the position of the luma intra predictionmode, the following process applies:

-   If a value of intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2] is equal    to 1 or if CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2] is equal to    MODE_IBC or MODE_PLT, lumaIntraPredMode is set equal to    INTRA_PLANAR.-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

In one embodiment of the present disclosure, a position of IBC or MIP orpalette flags are aligned with the position of the luma intra predictionmode, the following process applies:

-   If a value of intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2] is equal    to 1 or if CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2] is equal to    MODE_IBC or MODE_PLT, lumaIntraPredMode is set equal to INTRA_DC.-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

In one embodiment of the present disclosure, a position of IBC or MIP orpalette flags are aligned with the position of the luma intra predictionmode, the following process applies:

-   if CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2] is equal to MODE_IBC    or MODE_PLT, lumaIntraPredMode is set equal to INTRA_DC-   Otherwise if a value of intra_mip_flag[xCb+cbWidth/2]    [yCb+cbHeight/2] is equal to 1, lumaIntraPredMode is set equal to    INTRA_PLANAR.-   Otherwise, lumaIntraPredMode is set equal to    IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

In above embodiments, CuPredMode[xCb+cbWidth/2][yCb+cbHeight/2] orCuPredMode[i][xCb+cbWidth/2][yCb+cbHeight/2] is used. In fact, theyspecify the same thing, i.e., the prediction mode at position(xCb+cbWidth/2, yCb+cbHeight/2) of the luma components. NotesCuPredMode[i][xCb+cbWidth/2][yCb+cbHeight/2] is used with one moredimension of specifying luma or chroma components, wherein i=0 or 1.CuPredMode[0] [xCb+cbWidth/2][yCb+cbHeight/2] represents the predictionmode of luma component since its dimension index is 0. If a chromachannel is used, the corresponding variable would beCuPredMode[1][xCb+cbWidth/2][yCb+cbHeight/2].

In above embodiment, when CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2]is equal to MODE_PLT, it indicates the luma component at the lumaposition (cbWidth/2, cbHeight/2) uses palette mode. The luma position(cbWidth/2, cbHeight/2) specifies the position relative to the top-leftluma sample of the current coding block. The top-left sample of thecurrent coding block (xCb, yCb) specifies the position relative to thetop left sample of the current picture.

An example of the luma position (xCb+cbWidth/2, yCb+cbHeight/2) isillustrated in FIG. 7, where xCb=128, yCb=64, cbWidth=64, cbHeight=32.

In particular, the following methods and embodiments implemented by adecoding or encoding device. The decoding device may be video decoder 30of FIG. 1A, or decoder 30 of FIG. 3. The encoding device may be videoencoder 20 of FIG. 1A, or encoder 20 of FIG. 2.

According to an embodiment 900 (see FIG. 9), the device obtains firstindication information for a luma position (cbWidth/2, cbHeight/2) of acurrent coding block, relative to a top-left luma sample position (xCb,yCb) of the current coding block, where cbWidth represents a width ofthe current coding block in a luma component, and cbHeight represents aheight of the current coding block in the luma component at operation901. Correspondingly, cbWidth/2 represents a half of the width of thecurrent coding block in a luma component, and cbHeight/2 represents ahalf of the height of the current coding block in the luma component.The absolute position of the luma position (cbWidth/2, cbHeight/2) is(xCb+cbWidth/2, yCb+cbHeight/2), i.e., the ‘middle’ of the correspondingluma prediction block.

For example, the first indication information for the luma position(cbWidth/2, cbHeight/2) may beintra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2].

At operation 902, when the first indication information indicates that aMatrix-based Intra Prediction, MIP, is applied for the luma component atthe luma position (cbWidth/2, cbHeight/2), relative to the top-left lumasample position (xCb, yCb) of the current coding block, the device setsa value of a luma intra prediction mode associated with the currentcoding block to a first default value. For example, the first defaultvalue is the value of Planar mode.

When intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2] equals to 1, thefirst indication information indicates that the MIP is applied for theluma component.

At operation 903, when the first indication information indicates thatthe MIP is not applied for the luma component at the luma position(cbWidth/2, cbHeight/2), relative to the top-left luma sample position(xCb, yCb) of the current coding block, the device obtains secondindication information for the luma position (cbWidth/2, cbHeight/2) ofthe current coding block, relative to the top-left luma sample position(xCb, yCb) of the current coding block.

When intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2] equals to 0, thefirst indication information indicates that the MIP is not applied forthe luma component.

The second information for the luma position (cbWidth/2, cbHeight/2) maybe CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2].

At operation 905, when the second indication information indicates thatan Intra Block Copy, IBC, mode or palette mode is applied for the lumacomponent at the luma position (cbWidth/2, cbHeight/2), relative to thetop-left luma sample position (xCb, yCb) of the current coding block,the device sets the value of the luma intra prediction mode associatedwith the current coding block to a second default value. For example,the second default value is the value of DC mode.

When CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2] equals to MODE_IBC,the second indication information indicates that IBC mode is applied forthe luma component when CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2]equals to MODE_PLT, the second indication information indicates thatpalette mode is applied for the luma component.

When the second indication information indicates that IBC mode orpalette mode is not applied for the luma component at the luma position(cbWidth/2, cbHeight/2), the luma intra prediction mode associated withthe current coding block is set equal to luma intra prediction mode atposition [xCb+cbWidth/2][yCb+cbHeight/2], i.e.,

IntraPredModeY[xCb+cbWidth/2][yCb+cbHeight/2].

At operation 907, the device obtains a value of a chroma intraprediction mode based on the value of the luma intra prediction mode ofthe current coding block. If the value of the luma intra prediction modeof the current coding block is the first default value shown atoperation 902, the device obtains the value of the chroma intraprediction mode based on the first default value. If the value of theluma intra prediction mode of the current coding block is the seconddefault value shown at operation 905, the device obtains the value ofthe chroma intra prediction mode based on the second default value.

Detailed information for chroma intra prediction mode derivation byusing intra prediction mode from corresponding luma component is shownin the above-mentioned embodiments.

FIG. 10 illustrates embodiments of a device 1000. The device 1000 may bevideo decoder 30 of FIG. 1A, or decoder 30 of FIG. 3, or may be videoencoder 20 of FIG. 1A, or encoder 20 of FIG. 2. The device 1000 can beused to implement the embodiment 900, and the other embodimentsdescribed above.

The device 1000 for obtaining chroma intra prediction mode, includes anobtaining unit 1001, a setting unit 1002, and a chroma intra predictionmode unit 1003. The obtaining unit 1001, configured to obtain firstindication information for a luma position (cbWidth/2, cbHeight/2) of acurrent coding block, relative to a top-left luma sample position (xCb,yCb) of the current coding block, where cbWidth represents a width ofthe current coding block in a luma component, cbHeight represents aheight of the current coding block in the luma component. The settingunit 1002, configured to set a value of a luma intra prediction modeassociated with the current coding block to a first default value, whenthe first indication information indicates that a Matrix-based IntraPrediction, MIP, is applied for the luma component at the luma position(cbWidth/2, cbHeight/2), relative to the top-left luma sample position(xCb, yCb) of the current coding block.

The obtaining unit 1001, further configured to obtain second indicationinformation for the luma position (cbWidth/2, cbHeight/2) of the currentcoding block, when the first indication information indicates that theMIP is not applied for the luma component at the luma position(cbWidth/2, cbHeight/2), relative to the top-left luma sample position(xCb, yCb) of the current coding block.

The setting unit 1002, further configured to set the value of the lumaintra prediction mode associated with the current coding block to asecond default value when the second indication information indicatesthat an Intra Block Copy, IBC, mode or palette mode is applied for theluma component at the luma position (cbWidth/2, cbHeight/2), relative tothe top-left luma sample position (xCb, yCb) of the current coding block

The chroma intra prediction mode unit 1003, configured to obtain a valueof a chroma intra prediction mode based on the value of the luma intraprediction mode of the current coding block.

The present disclosure provides the following set of embodiments oraspects:

According to a first aspect the disclosure relates to a method of codingimplemented by a decoding device, comprising:

obtaining a value of a first indication information for the currentcoding block, wherein the value of the first indication information forthe current coding block is derived from the luma componentcorresponding to a luma position (cbWidth/2, cbHeight/2), relative to atop-left luma sample of the current coding block (xCb, yCb), cbWidthrepresents a width of the current coding block in luma samples, cbHeightrepresents a height of the current coding block in luma samples;

setting a value of a luma intra prediction mode associated with thecurrent coding block to a first default value, when the value of thefirst indication information indicates that a Matrix-based IntraPrediction, MIP, is applied for the luma component at the luma position(cbWidth/2, cbHeight/2), relative to the top-left luma sample of thecurrent coding block (xCb, yCb);

obtaining a value of a chroma intra prediction mode based on the valueof the luma intra prediction mode of the current coding block.

According to a second aspect the disclosure relates to a method ofcoding implemented by a decoding device, comprising:

obtaining a value of a first indication information for the currentcoding block, wherein the value of the first indication information forthe current coding block is derived from the luma componentcorresponding to a luma position (cbWidth/2, cbHeight/2), relative to atop-left luma sample of the current coding block (xCb, yCb), and whereincbWidth represents a width of the current coding block in luma samples,cbHeight represents a height of the current coding block in lumasamples;

setting a value of a luma intra prediction mode associated with thecurrent coding block to a first default value, when the value of thefirst indication information indicates that an Intra Block Copy, IBC,mode or palette mode is applied for luma component at the luma position(cbWidth/2, cbHeight/2), relative to a top-left luma sample of thecurrent coding block (xCb, yCb);

obtaining a value of a chroma intra prediction mode based on the valueof the luma intra prediction mode of the current coding block.

As discussed above, in the conventional cases related to MIP, or IBC,or, palette (as the example shown in FIG. 7), there is a misalignmentbetween mode MIP's (or IBC's, or palette's) position and luma intraprediction mode's position when the partition of luma component isdifferent from the partition of chroma component (e.g. when dual-treecoding method is enabled). In the aspects and implementation forms ofthe disclosure, obtaining first indication information from a fixedposition (cbWidth/2, cbHeight/2) in the corresponding luma componentensures mode MIP's position and luma intra prediction mode's position isaligned when in a given block size, the partition of luma component isdifferent from the partition of chroma component (e.g. when dual-treecoding method is enabled). When the first indication information doesnot indicate that MIP is applied for the luma component at the lumaposition (cbWidth/2, cbHeight/2), obtaining second indicationinformation from a fixed position (cbWidth/2, cbHeight/2) in thecorresponding luma component ensures mode IBC's position and luma intraprediction mode's position is aligned when in a given block size, thepartition of luma component is different from the partition of chromacomponent (e.g. when dual-tree coding method is enabled). Alternatively,obtaining second indication information from a fixed position(cbWidth/2, cbHeight/2) in the corresponding luma component ensures modepalette's position and luma intra prediction mode's position is alignedwhen in a given block size, the partition of luma component is differentfrom the partition of chroma component (e.g. when dual-tree codingmethod is enabled).

Following is an explanation of the applications of the encoding methodas well as the decoding method as shown in the above-mentionedembodiments, and a system using them.

FIG. 11 is a block diagram showing a content supply system 3100 forrealizing content distribution service. This content supply system 3100includes capture device 3102, terminal device 3106, and optionallyincludes display 3126. The capture device 3102 communicates with theterminal device 3106 over communication link 3104. The communicationlink may include the communication channel 13 described above. Thecommunication link 3104 includes but not limited to WIFI, Ethernet,Cable, wireless (3G/4G/5G), USB, or any kind of combination thereof, orthe like.

The capture device 3102 generates data, and may encode the data by theencoding method as shown in the above embodiments. Alternatively, thecapture device 3102 may distribute the data to a streaming server (notshown in the Figures), and the server encodes the data and transmits theencoded data to the terminal device 3106. The capture device 3102includes but not limited to camera, smart phone or Pad, computer orlaptop, video conference system, PDA, vehicle mounted device, or acombination of any of them, or the like. For example, the capture device3102 may include the source device 12 as described above. When the dataincludes video, the video encoder 20 included in the capture device 3102may actually perform video encoding processing. When the data includesaudio (i.e., voice), an audio encoder included in the capture device3102 may actually perform audio encoding processing. For some practicalscenarios, the capture device 3102 distributes the encoded video andaudio data by multiplexing them together. For other practical scenarios,for example in the video conference system, the encoded audio data andthe encoded video data are not multiplexed. Capture device 3102distributes the encoded audio data and the encoded video data to theterminal device 3106 separately.

In the content supply system 3100, the terminal device 310 receives andreproduces the encoded data. The terminal device 3106 could be a devicewith data receiving and recovering capability, such as smart phone orPad 3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, set top box (STB) 3116, videoconference system 3118, video surveillance system 3120, personal digitalassistant (PDA) 3122, vehicle mounted device 3124, or a combination ofany of them, or the like capable of decoding the above-mentioned encodeddata. For example, the terminal device 3106 may include the destinationdevice 14 as described above. When the encoded data includes video, thevideo decoder 30 included in the terminal device is prioritized toperform video decoding. When the encoded data includes audio, an audiodecoder included in the terminal device is prioritized to perform audiodecoding processing.

For a terminal device with its display, for example, smart phone or Pad3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, personal digital assistant (PDA)3122, or vehicle mounted device 3124, the terminal device can feed thedecoded data to its display. For a terminal device equipped with nodisplay, for example, STB 3116, video conference system 3118, or videosurveillance system 3120, an external display 3126 is contacted thereinto receive and show the decoded data.

When each device in this system performs encoding or decoding, thepicture encoding device or the picture decoding device, as shown in theabove-mentioned embodiments, can be used.

FIG. 12 is a diagram showing a structure of an example of the terminaldevice 3106. After the terminal device 3106 receives stream from thecapture device 3102, the protocol proceeding unit 3202 analyzes thetransmission protocol of the stream. The protocol includes but notlimited to Real Time Streaming Protocol (RTSP), Hyper Text TransferProtocol (HTTP), HTTP Live streaming protocol (HLS), MPEG-DASH,Real-time Transport protocol (RTP), Real Time Messaging Protocol (RTMP),or any kind of combination thereof, or the like.

After the protocol proceeding unit 3202 processes the stream, streamfile is generated. The file is outputted to a demultiplexing unit 3204.The demultiplexing unit 3204 can separate the multiplexed data into theencoded audio data and the encoded video data. As described above, forsome practical scenarios, for example in the video conference system,the encoded audio data and the encoded video data are not multiplexed.In this situation, the encoded data is transmitted to video decoder 3206and audio decoder 3208 without through the demultiplexing unit 3204.

Via the demultiplexing processing, video elementary stream (ES), audioES, and optionally subtitle are generated. The video decoder 3206, whichincludes the video decoder 30 as explained in the above mentionedembodiments, decodes the video ES by the decoding method as shown in theabove-mentioned embodiments to generate video frame, and feeds this datato the synchronous unit 3212. The audio decoder 3208, decodes the audioES to generate audio frame, and feeds this data to the synchronous unit3212. Alternatively, the video frame may store in a buffer (not shown inFIG. 12) before feeding it to the synchronous unit 3212. Similarly, theaudio frame may store in a buffer (not shown in FIG. 12) before feedingit to the synchronous unit 3212.

The synchronous unit 3212 synchronizes the video frame and the audioframe, and supplies the video/audio to a video/audio display 3214. Forexample, the synchronous unit 3212 synchronizes the presentation of thevideo and audio information. Information may code in the syntax usingtime stamps concerning the presentation of coded audio and visual dataand time stamps concerning the delivery of the data stream itself.

If subtitle is included in the stream, the subtitle decoder 3210 decodesthe subtitle, and synchronizes it with the video frame and the audioframe, and supplies the video/audio/subtitle to a video/audio/subtitledisplay 3216.

The present disclosure is not limited to the above-mentioned system, andeither the picture encoding device or the picture decoding device in theabove-mentioned embodiments can be incorporated into other system, forexample, a car system.

Mathematical Operators

The mathematical operators used in this application are similar to thoseused in the C programming language. However, the results of integerdivision and arithmetic shift operations are defined more precisely, andadditional operations are defined, such as exponentiation andreal-valued division. Numbering and counting conventions generally beginfrom 0, e.g., “the first” is equivalent to the 0-th, “the second” isequivalent to the 1-th, etc.

Arithmetic Operators

The following arithmetic operators are defined as follows:

-   + Addition-   − Subtraction (as a two-argument operator) or negation (as a unary    prefix operator)-   * Multiplication, including matrix multiplication-   x^(y) Exponentiation. Specifies x to the power of y. In other    contexts, such notation is used for superscripting not intended for    interpretation as exponentiation.-   / Integer division with truncation of the result toward zero. For    example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4 are    truncated to −1.-   ÷ Used to denote division in mathematical equations where no    truncation or rounding is intended.

$\frac{x}{y}$

Used to denote division in mathematical equations where no truncation orrounding is intended.

$\sum\limits_{i = x}^{y}{f(i)}$

The summation of f(i) with i taking all integer values from x up to andincluding y.

-   x % y Modulus. Remainder of x divided by y, defined only for    integers x and y with x>=0 and y>0.

Logical Operators

The following logical operators are defined as follows:

-   x && y Boolean logical “and” of x and y-   x⊕y Boolean logical “or” of x and y-   ! Boolean logical “not”-   x? y:z If x is TRUE or not equal to 0, evaluates to the value of y;    otherwise, evaluates to the value of z.

Relational Operators

The following relational operators are defined as follows:

-   > Greater than-   >= Greater than or equal to-   < Less than-   <= Less than or equal to-   == Equal to-   != Not equal to

When a relational operator is applied to a syntax element or variablethat has been assigned the value “na” (not applicable), the value “na”is treated as a distinct value for the syntax element or variable. Thevalue “na” is considered not to be equal to any other value.

Bit-Wise Operators

The following bit-wise operators are defined as follows:

-   & Bit-wise “and”. When operating on integer arguments, operates on a    two's complement representation of the integer value. When operating    on a binary argument that contains fewer bits than another argument,    the shorter argument is extended by adding more significant bits    equal to 0.-   | Bit-wise “or”. When operating on integer arguments, operates on a    two's complement representation of the integer value. When operating    on a binary argument that contains fewer bits than another argument,    the shorter argument is extended by adding more significant bits    equal to 0.-   {circumflex over ( )} A Bit-wise “exclusive or”. When operating on    integer arguments, operates on a two's complement representation of    the integer value. When operating on a binary argument that contains    fewer bits than another argument, the shorter argument is extended    by adding more significant bits equal to 0.-   x>>y Arithmetic right shift of a two's complement integer    representation of x by y binary digits. This function is defined    only for non-negative integer values of y. Bits shifted into the    most significant bits (MSBs) as a result of the right shift have a    value equal to the MSB of x prior to the shift operation.-   x>>y Arithmetic left shift of a two's complement integer    representation of x by y binary digits. This function is defined    only for non-negative integer values of y. Bits shifted into the    least significant bits (LSBs) as a result of the left shift have a    value equal to 0.

Assignment Operators

The following arithmetic operators are defined as follows:

-   = Assignment Operator-   ++ Increment, i.e., x++ is equivalent to x=x+1; when used in an    array index, evaluates to the value of the variable prior to the    increment operation.-   −− Decrement, i.e., x−− is equivalent to x=x−1; when used in an    array index, evaluates to the value of the variable prior to the    decrement operation.-   += Increment by amount specified, i.e., x+=3 is equivalent to x=x+3,    and x+=(−3) is equivalent to x=x+(−3).-   −= Decrement by amount specified, i.e., x−=3 is equivalent to x=x−3,    and x−=(−3) is equivalent to x=x−(−3).

Range Notation

The following notation is used to specify a range of values:

-   x=y . . . z x takes on integer values starting from y to z,    inclusive, with x, y, and z being integer numbers and z being    greater than y.

Mathematical Functions

The following mathematical functions are defined:

${{Abs}(x)} = \left\{ \begin{matrix}x & ; & {x>=0} \\{- x} & ; & {x < 0}\end{matrix} \right.$

-   Asin(x) the trigonometric inverse sine function, operating on an    argument x that is in the range of −1.0 to 1.0, inclusive, with an    output value in the range of −π÷2 to π÷2, inclusive, in units of    radians-   Atan(x) the trigonometric inverse tangent function, operating on an    argument x, with an output value in the range of −π÷2 to π÷2,    inclusive, in units of radians

${{Atan}2\left( {y,x} \right)} = \left\{ \begin{matrix}{{Atan}\left( \frac{y}{x} \right)} & ; & {x > 0} \\{{{Atan}\left( \frac{y}{x} \right)} + \pi} & ; & {{x < 0}\&\&{y>=0}} \\{{{Atan}\left( \frac{y}{x} \right)} - \pi} & ; & {{x < 0}\&\&{y < 0}} \\{+ \frac{\pi}{2}} & ; & {{x==0}\&\&{y>=0}} \\{- \frac{\pi}{2}} & ; & {otherwise}\end{matrix} \right.$

-   Ceil(x) the smallest integer greater than or equal to x.-   Clip1_(Y)(x)=Clip3(0, (1<<BitDepth_(Y))−1, x)-   Clip1_(C)(x)=Clip3(0, (1<<BitDepth_(C))−1, x)

${{Clip}3\left( {x,y,z} \right)} = \left\{ \begin{matrix}x & ; & {z < x} \\y & ; & {z > y} \\z & ; & {otherwise}\end{matrix} \right.$

-   Cos(x) the trigonometric cosine function operating on an argument x    in units of radians-   Floor(x) the largest integer less than or equal to x.

${{GetCurrMsb}\left( {a,b,c,d} \right)} = \left\{ \begin{matrix}{c + d} & ; & {b - {a>=d/2}} \\{c - d} & ; & {{a - b} > {d/2}} \\c & ; & {otherwise}\end{matrix} \right.$

-   Ln(x) the natural logarithm of x (the base-e logarithm, where e is    the natural logarithm base constant 2.718 281 828 . . . ).-   Log2(x) the base-2 logarithm of x.-   Log10(x) the base-10 logarithm of x.

${{Min}\left( {x,y} \right)} = \left\{ {{\begin{matrix}x & ; & {x<=y} \\y & ; & {x > y}\end{matrix}{{Max}\left( {x,y} \right)}} = \left\{ \begin{matrix}x & ; & {x>=y} \\y & ; & {x < y}\end{matrix} \right.} \right.$

-   Round(x)=Sign(x)*Floor(Abs(x)+0.5)

${{Sign}(x)} = \left\{ \begin{matrix}1 & ; & {x > 0} \\0 & ; & {x==0} \\{- 1} & ; & {x < 0}\end{matrix} \right.$

-   Sin(x) the trigonometric sine function operating on an argument x in    units of radians-   Sqrt(x)=√{square root over (x)}-   Swap(x, y)=(y, x)-   Tan(x) the trigonometric tangent function operating on an argument x    in units of radians

Order of Operation Precedence

When an order of precedence in an expression is not indicated explicitlyby use of parentheses, the following rules apply:

-   Operations of a higher precedence are evaluated before any operation    of a lower precedence.-   Operations of the same precedence are evaluated sequentially from    left to right.

The table below specifies the precedence of operations from highest tolowest; a higher position in the table indicates a higher precedence.

For those operators that are also used in the C programming language,the order of precedence used in this Specification is the same as usedin the C programming language.

TABLE Operation precedence from highest (at top of table) to lowest (atbottom of table) operations (with operands x, y, and z) ″x++″, ″x− −″″!x″, ″−x″ (as a unary prefix operator) x^(y) ″x * y″, ″x / y″, ″x ÷ y″,″ x/y, ″x % y″ ″x + y″, ″x − y″ (as a two-argument operator),$\underset{\text{“i”}\text{“=”}\text{“x”}}{\overset{\text{“y”}}{\text{“∑”}}}\text{“f(i)”}$″x << y″, ″x >> y″ ″x < y″, ″x <= y″, ″x > y″, ″x >=y″ ″x = =y″, ″x !=y″ ″x & y″ ″x | y″ ″x && y″ ″x | | y″ ″x ? y:z″ ″x..y″ ″x = y″, ″x +=y″, ″x −= y″

Text Description of Logical Operations

In the text, a statement of logical operations as would be describedmathematically in the following form:

if( condition 0 )  statement 0 else if( condition 1 )  statement 1 ...else /* informative remark on remaining condition */  statement n   maybe described in the following manner:  ... as follows / ... thefollowing applies:  - If condition 0, statement 0  - Otherwise, ifcondition 1, statement 1  - ...  - Otherwise (informative remark onremaining condition), statement n

Each “If . . . Otherwise, if . . . Otherwise, . . . ” statement in thetext is introduced with “. . . as follows” or “. . . the followingapplies” immediately followed by “If . . . ”. The last condition of the“If . . . Otherwise, if . . . Otherwise, . . . ” is always an“Otherwise, . . . ”. Interleaved “If . . . Otherwise, if . . .Otherwise, . . . ” statements can be identified by matching “. . . asfollows” or “. . . the following applies” with the ending “Otherwise, .. . ”.

In the text, a statement of logical operations as would be describedmathematically in the following form:

if( condition 0a && condition 0b )  statement 0 else if( condition 1a ||condition 1b )  statement 1 ... else  statement n   may be described inthe following manner:  ... as follows / ... the following applies:   -If all of the following conditions are true, statement 0:    - condition 0a    -  condition 0b   - Otherwise, if one or more of thefollowing conditions are true, statement 1:    -  condition 1a    - condition 1b   - ...   - Otherwise, statement n

In the text, a statement of logical operations as would be describedmathematically in the following form:

if( condition 0 )  statement 0 if( condition 1 )  statement 1   may bedescribed in the following manner:  When condition 0, statement 0  Whencondition 1, statement 1.

Although embodiments of the disclosure have been primarily describedbased on video coding, it should be noted that embodiments of the codingsystem 10, encoder 20 and decoder 30 (and correspondingly the system 10)and the other embodiments described herein may also be configured forstill picture processing or coding, i.e. the processing or coding of anindividual picture independent of any preceding or consecutive pictureas in video coding. In general only inter-prediction units 244 (encoder)and 344 (decoder) may not be available in case the picture processingcoding is limited to a single picture 17. All other functionalities(also referred to as tools or technologies) of the video encoder 20 andvideo decoder 30 may equally be used for still picture processing, e.g.residual calculation 204/304, transform 206, quantization 208, inversequantization 210/310, (inverse) transform 212/312, partitioning 262/362,intra-prediction 254/354, and/or loop filtering 220, 320, and entropycoding 270 and entropy decoding 304.

Embodiments, e.g. of the encoder 20 and the decoder 30, and functionsdescribed herein, e.g. with reference to the encoder 20 and the decoder30, may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on a computer-readable medium or transmitted over communicationmedia as one or more instructions or code and executed by ahardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limiting, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

What is claimed is:
 1. A method of coding, comprising: obtainingindication information for a luma position (cbWidth/2, cbHeight/2) of acurrent coding block, relative to a top-left luma sample position (xCb,yCb) of the current coding block, wherein cbWidth represents a width ofthe current coding block in a luma component, cbHeight represents aheight of the current coding block in the luma component; setting avalue of a luma intra prediction mode associated with the current codingblock to a first default value, when the indication informationindicates that an Intra Block Copy (IBC) mode or palette mode is appliedfor the luma component at the luma position (cbWidth/2, cbHeight/2),relative to the top-left luma sample position (xCb, yCb) of the currentcoding block; and obtaining a value of a chroma intra prediction modebased on the value of the luma intra prediction mode of the currentcoding block.
 2. The method of claim 1, wherein the first default valueequals to a value of DC mode.
 3. The method of claim 1, wherein apartition of the luma component and a partition of a chroma component ofthe current coding block are not aligned.
 4. The method of claim 1,further comprising: setting the value of the luma intra prediction modeof the current coding block to a second default value, when aMatrix-based Intra Prediction (MIP) is applied for the luma component atthe luma position (cbWidth/2, cbHeight/2) and the indication informationindicates that an IBC mode or palette mode is not applied for the lumaposition (cbWidth/2, cbHeight/2).
 5. The method of claim 4, wherein thesecond default value equals to a value of Planar mode.
 6. The method ofclaim 1, wherein an absolute position of the luma position (cbWidth/2,cbHeight/2) is (xCb+cbWidth/2, yCb+cbHeight/2), the absolute position(xCb+cbWidth/2, yCb+cbHeight/2) specifying a position relative to a topleft sample of a current picture; the luma position (cbWidth/2,cbHeight/2) specifies a position relative to the top-left luma sampleposition (xCb, yCb) of the current coding block.
 7. The method of claim4, wherein when a value of intra_mip_flag[xCb+cbWidth/2][yCb+cbHeight/2]is equal to 1, the MIP is applied for the luma position (cbWidth/2,cbHeight/2).
 8. The method of claim 1, wherein whenCuPredMode[0][xCb+cbWidth/2] [yCb+cbHeight/2] is equal to MODE_IBC orMODE_PLT, respectively, the IBC mode or palette mode is applied for theluma position (cbWidth/2, cbHeight/2).
 9. A device for obtaining chromaintra prediction mode, comprising: one or more processors; and anon-transitory computer-readable storage medium coupled to theprocessors and storing programming for execution by the processors,wherein the programming, when executed by the processors, configures thedevice to: obtain indication information for a luma position (cbWidth/2,cbHeight/2) of a current coding block, relative to a top-left lumasample position (xCb, yCb) of the current coding block, wherein cbWidthrepresents a width of the current coding block in a luma component,cbHeight represents a height of the current coding block in the lumacomponent; set a value of a luma intra prediction mode associated withthe current coding block to a default value when the indicationinformation indicates that an Intra Block Copy (IBC) mode or palettemode is applied for the luma component at the luma position (cbWidth/2,cbHeight/2), relative to the top-left luma sample position (xCb, yCb) ofthe current coding block; and obtain a value of a chroma intraprediction mode based on the value of the luma intra prediction mode ofthe current coding block.
 10. The device of claim 9, wherein theindication information is CuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2].11. The device of claim 10, wherein whenCuPredMode[0][xCb+cbWidth/2][yCb+cbHeight/2] equals to MODE_IBC orMODE_PLT, the indication information indicates that IBC mode or palettemode is applied for the luma component.
 12. The device of claim 9,wherein the default value is a value of DC mode.
 13. The device of claim9, wherein a partition of the luma component and a partition of a chromacomponent of the current coding block are not aligned.
 14. The device ofclaim 9, wherein an absolute position of the luma position (cbWidth/2,cbHeight/2) is (xCb+cbWidth/2, yCb+cbHeight/2), the absolute position(xCb+cbWidth/2, yCb+cbHeight/2) specifying a position relative to a topleft sample of a current picture; the luma position (cbWidth/2,cbHeight/2) specifies a position relative to the top-left luma sampleposition (xCb, yCb) of the current coding block.
 15. A non-transitorystorage medium comprising a bitstream encoded by the operations of:obtaining indication information for a luma position (cbWidth/2,cbHeight/2) of a current coding block, relative to a top-left lumasample position (xCb, yCb) of the current coding block, wherein cbWidthrepresents a width of the current coding block in a luma component,cbHeight represents a height of the current coding block in the lumacomponent; setting a value of a luma intra prediction mode associatedwith the current coding block to a first default value, when theindication information indicates that an Intra Block Copy (IBC) mode orpalette mode is applied for the luma component at the luma position(cbWidth/2, cbHeight/2), relative to the top-left luma sample position(xCb, yCb) of the current coding block; and obtaining a value of achroma intra prediction mode based on the value of the luma intraprediction mode of the current coding block.